Technical Fiat Stilo 1.6 16v P0638 Error code

[aijosh]

Hello All,

I have this persistent P0638 error code.
When it comes on, the car goes into limp mode.

I use the OBD reader to clear the code and start up then it works ok for about a minute then the throws the P0638 and enters limp mode.

I can't seem to find what P0638 means.

Does anyone have a solution for this?

Thanks

 

[NebulaStilo]

Hello All,

I have this persistent P0638 error code.
When it comes on, the car goes into limp mode.

I use the OBD reader to clear the code and start up then it works ok for about a minute then the throws the P0638 and enters limp mode.

I can't seem to find what P0638 means.

Does anyone have a solution for this?

Thanks

Hi
I have the exact same problem.

What is your symptoms?

Lack of power?
Slow acceleration?
Surge on acceleration?
Car won't rev to full potential ie 6000rpm I think it is. Only revs up until around 5000rpm

Let me know

Thanks.

 

[aijosh]

Hi
Lack of power?
Slow acceleration?
Surge on acceleration?
Car won't rev to full potential ie 6000rpm I think it is. Only revs up until around 5000rpm

Yes. Something of this sort though not exactly the same.
I believe I already stated that in my post.
The car goes into LIMP MODE which generally looks like what you stated above or gets triggered after all the behaviours you stated have been exhibited.

What really happens though is that the throttle sticks to around 2,000rpm to 2,500rpm and stops working. So when you press the throttle it doesn't work at all (It allows you to still rev about 500rpm - 1000rpm extra though).

The car at times can be taken out of LIMP mode by turning key off and back on. This can give you about 30secs to 3mins of normal driving before LIMP mode is triggered again.

====================================
What I've done from MOST LIKELY to least likely was:

.1 Push up and re-solder dropped pins on ECU ---- FAIL
.2 Cleaned ECU connectors with Contact Cleaner ---- FAIL
.3 Cleaned TPS in Throttle body with contact cleaner ---- FAIL
.4 Clean Throttle body with Carburetor Cleaner ---- FAIL
.5 Cleaned all connectors under the fuse-box behind the battery ---- FAIL
.6 Cleaned D4 connector with contact cleaner ---- FAIL
.7 Removed yellow plastic on D4, inspected and decided to pull out the pins that looked like they were too wide. Pressed them together and fix back in and coupled D4 back ---- FAIL
.8 :bang: :bang: :bang:
.9
.10 Tried 4 different older throttle body to be sure its not the current one triggering P0638... Confirmed P0638 on all of them including their own error code so I'm sure its not the current throttle body. So.. ---- FAIL
.11 :bang:
.12 Returned the old spark plugs ---- SUCCESS
=======

From my research P0638 seems to be symptoms of a bad ECU that's why I went for the ECU first.
You probably have a malfunctioning ECU too or some loose connections either in the harness or the connectors.
A bad throttle body is also a possible cause.

Let me know your experience in fixing your issue and solutions that you might have suggested to me assuming I had not found a fix for my issue.

I'm still skeptical about my fix because the car's idle is still not that great and it also still cuts out when decelerating to a stop from high speed

Thanks

 

[NebulaStilo]

Yes. Something of this sort though not exactly the same.
I believe I already stated that in my post.
The car goes into LIMP MODE which generally looks like what you stated above or gets triggered after all the behaviours you stated have been exhibited.

What really happens though is that the throttle sticks to around 2,000rpm to 2,500rpm and stops working. So when you press the throttle it doesn't work at all (It allows you to still rev about 500rpm - 1000rpm extra though).

The car at times can be taken out of LIMP mode by turning key off and back on. This can give you about 30secs to 3mins of normal driving before LIMP mode is triggered again.

====================================
What I've done from MOST LIKELY to least likely was:

.1 Push up and re-solder dropped pins on ECU ---- FAIL
.2 Cleaned ECU connectors with Contact Cleaner ---- FAIL
.3 Cleaned TPS in Throttle body with contact cleaner ---- FAIL
.4 Clean Throttle body with Carburetor Cleaner ---- FAIL
.5 Cleaned all connectors under the fuse-box behind the battery ---- FAIL
.6 Cleaned D4 connector with contact cleaner ---- FAIL
.7 Removed yellow plastic on D4, inspected and decided to pull out the pins that looked like they were too wide. Pressed them together and fix back in and coupled D4 back ---- FAIL
.8 :bang: :bang: :bang:
.9
.10 Tried 4 different older throttle body to be sure its not the current one triggering P0638... Confirmed P0638 on all of them including their own error code so I'm sure its not the current throttle body. So.. ---- FAIL
.11 :bang:
.12 Returned the old spark plugs ---- SUCCESS
=======

From my research P0638 seems to be symptoms of a bad ECU that's why I went for the ECU first.
You probably have a malfunctioning ECU too or some loose connections either in the harness or the connectors.
A bad throttle body is also a possible cause.

Let me know your experience in fixing your issue and solutions that you might have suggested to me assuming I had not found a fix for my issue.

I'm still skeptical about my fix because the car's idle is still not that great and it also still cuts out when decelerating to a stop from high speed

Thanks

Hi

Yes she does go into limp mode. I don't experience limp mode that often though like you.
I would say once or twice a week she would go into limp mode from startup and like you say,would not rev over 2000rpm.

I would whip out code reader and clear codes which is always p0638 which pertains to Throttle body actuator.
After that I switch off and on then she's good to go.

My loss of power could be because I have a bad clutch I must replace?but the throttle body problem I think is adding to that.

I replaced spark plugs
O2 sensor
Changed oil filter and oil
Air filter
Fuel filter and pump
Also cleaned throttle body,thoroughly.
Changed 2 coil packs so far
Performed a compression test too and that's in the 190's so that's good.

Which plugs Are you using? I also changed plugs and drove much better but then started again with uneven acceleration ie surge on acceleration.

And i too have a not so great idle

None if this helped.

I haven't tried a different throttle body though.

At times she will be really responsive and move like I know she does but at times shes really dead.

I saw on the forum there is a ECU update for the 1.6 that includes the TPS and the MAP sensor.
The TPS is known to be an issue on the 1.6

Check your live data from the TPS in percentage and see what it does. Is it smooth incline as you accelerate or does it jump like mine does. If it jumps then it can point towards a bad TPS


Don't worry so much about the sudden spikes and immediate drops,I was driving on highway dodging through cars so that can be me accelerating and decelerating. Take note of the gradual spike or steady acceleration. Doesn't stay smooth. This is making me believe it's the TPS. I want to try a second hand one to see what it does before buying a new one.

Hope this helps as much as your post cleared things up for me.

 

[aijosh]

Thanks.

What app do you use to check the live data for the TPS. I can't find live data option in mine?


====
From all indications P0638 means the ECU is confused or doesn't know what the problem is. So fixing this would be a hit or miss.

I'll suggest you change the throttle body and see what happens. The inability for the car to rev to 7,000 - 8,000rpm is most likely a problem with the TPS.... Although I noticed my Stilo always catches a bad TPS as it always indicates P1220, or 1221 on bad throttle body. So it might not be a bad throttle body since you are not getting P1220.

When trying a second-hand one, be sure you test it there to be sure it works before picking it up. The reason I have 4 extra throttle bodies is because I bought 3 bad ones + the old bad one making 4.

A good start is to clean the TPS itself. I believe you've cleaned the butterfly flap but you need to clean the sensor. You'll have to pry open the black portion and get to the sensor itself. There is a silver metal covering it which you'll pry open too before you finally get to it. Use electrical contact cleaner to thoroughly spray it out. ensure you dont break anything.
======

For the plugs. I'm now 100% sure using a wrong plug would surely stop the car from working properly. Its not the first time I've had this issue (the first time was when a mechanic tried to service the engine for me).

I'm not sure of what plugs I use. I'll check when I get home and add a picture of it.
What you can do is if you have the original plug that came with the car (the one labelled FIAT, just get to the market and look for one that is EXACTLY the same.

Any slight variation no matter how irrelevant it seems is a NO NO.

OR Better still just return the old ones, pending when you'll find where the real problem is.



====
OTHER ACTIONS unlikely but might help. You can try these as last steps before opening up your ECU to inspect if there are bad solder joints or dropped pins.
====

Clean the MAP sensor. Also try a spare one.

====

Check for vacuum leaks around manifold.

====

Change the crank sensor

 

[NebulaStilo]

Thanks.

What app do you use to check the live data for the TPS. I can't find live data option in mine?


====
From all indications P0638 means the ECU is confused or doesn't know what the problem is. So fixing this would be a hit or miss.

I'll suggest you change the throttle body and see what happens. The inability for the car to rev to 7,000 - 8,000rpm is most likely a problem with the TPS.... Although I noticed my Stilo always catches a bad TPS as it always indicates P1220, or 1221 on bad throttle body. So it might not be a bad throttle body since you are not getting P1220.

When trying a second-hand one, be sure you test it there to be sure it works before picking it up. The reason I have 4 extra throttle bodies is because I bought 3 bad ones + the old bad one making 4.

A good start is to clean the TPS itself. I believe you've cleaned the butterfly flap but you need to clean the sensor. You'll have to pry open the black portion and get to the sensor itself. There is a silver metal covering it which you'll pry open too before you finally get to it. Use electrical contact cleaner to thoroughly spray it out. ensure you dont break anything.
======

For the plugs. I'm now 100% sure using a wrong plug would surely stop the car from working properly. Its not the first time I've had this issue (the first time was when a mechanic tried to service the engine for me).

I'm not sure of what plugs I use. I'll check when I get home and add a picture of it.
What you can do is if you have the original plug that came with the car (the one labelled FIAT, just get to the market and look for one that is EXACTLY the same.

Any slight variation no matter how irrelevant it seems is a NO NO.

OR Better still just return the old ones, pending when you'll find where the real problem is.



====
OTHER ACTIONS unlikely but might help. You can try these as last steps before opening up your ECU to inspect if there are bad solder joints or dropped pins.
====

Clean the MAP sensor. Also try a spare one.

====

Check for vacuum leaks around manifold.

====

Change the crank sensor

Hi

I use torque app with Bluetooth elm obd2.

I do get a p1220 seldom but more a p0638.

I changed plugs to plugs part store has listed and it works on the car in terms of specs but it's not what is listed at NGK. Only difference between the two is one is 6 and other is 5 heat range.

What part is the TPS inside the throttle body.is the black part the actual TPS that's connected to the butterfly valve. I opened and cleaned the inside already and all checks out.

I do not have the fiat plugs. Previous owner already changed them.

I changed crank sensor to some aftermarket junk but returned the original because ran better with original on and the new one after a year was starting to throw a code and would crank long before it started. I changed crank sensor in first place just as a pre caution but didn't do anything.

No vacuum leaks seem to be present.

Do you perhaps have some pics of inside your throttle body so I can compare?

I see there is some sort of gear driven by butterfly valves motor that fits into a hole in the black part of the throttle body. There is some sort of metal piece that sends signal to the connector on the outside of the throttle body.
That's why I ask is the black part the Actual TPS.

On my code reader and on the net it says p0638 is throttle body actuator control range/performance.

I see it as the ECU isn't recognising the input from the Throttle actuator and sets the code.

Also I put 12v straight from battery onto butterfly motor and it opens all the way

 

[NebulaStilo]

See the protruding piece on the gear goes into the potentiometer. As you will know. The potentiometer pic, i take it that is the TPS itself.

My potentiometer as labeled has play in it if you try and move it with your fingers. Like you can wiggle it all around. It doesn't just turn like you would think logically from the protruding piece of gear,it also can be moved from side to side. Basically sits loose. Is that supposed to be like that or must it ONLY turn not move up and down. Feels like a loose nail in a wood. If that makes sense???

 

[aijosh]

https://www.dropbox.com/s/zhjjmwxiv83oh7n/3.jpg

Just get behind the potentiometer. And clean that. I think it has some sort of silicon grease in it. But... I normally just clean everything out.

Your issue is most likely a failing throttle body.

===
The play is not an issue. I believe its because its open. The rod that goes into it should stop the up and down play when its closed.
Its movement is rotational, clockwise/anticlockwise. It doesnt go all the way round, just about 120degrees thereabout

==
Another likely issue could be the sensor in your throttle pedal itself but I don't think this is the issue.
If changing the throttle body doesn't solve it then its probably poor connections in the wiring harness between the ECU and other components of the car. Thats a serious pain to fix cos it'll most likely be intermittent and would work if you wiggle the wires the right way.

===
Forgot to check the plugs and the car has been taken out.

 

[NebulaStilo]

https://www.dropbox.com/s/zhjjmwxiv83oh7n/3.jpg

Just get behind the potentiometer. And clean that. I think it has some sort of silicon grease in it. But... I normally just clean everything out.

Your issue is most likely a failing throttle body.

===
The play is not an issue. I believe its because its open. The rod that goes into it should stop the up and down play when its closed.
Its movement is rotational, clockwise/anticlockwise. It doesnt go all the way round, just about 120degrees thereabout

==
Another likely issue could be the sensor in your throttle pedal itself but I don't think this is the issue.
If changing the throttle body doesn't solve it then its probably poor connections in the wiring harness between the ECU and other components of the car. Thats a serious pain to fix cos it'll most likely be intermittent and would work if you wiggle the wires the right way.

===
Forgot to check the plugs and the car has been taken out.

Ive never got that far in stripping the throttle body lol.

I didn't know it can go that far. I'm scared I might break something so could you perhaps show me a step by step as to how to remove it and what to look out for etc. Thanks.

I will be able to do it sometime in the week as she is a daily driver.

This morning I done live data again and when I accelerate or engine is under bigger load then at times the TPS will drop slightly and return back up but still not 100% stable.

Then if you accelerate hard it will also drop suddenly then up to where it's supposed to be

Thanks

 

[aijosh]

Well... I really can't help when it comes to that. I believe there would be a proper tool for removing it but I don't have that so I just take a knife OR a strong tiny flat screwdriver and force it out.

The metal always bends at the location where I pry and some of the plastic also chips away but.... that's life.

Its just a cover (I think) and its flexible so it can be bent back in place. So there is not much to fear.

Depending on how you pry it you might need to apply a lot of force to lift it off.

I usually look for a point at the outer edge, lift it, stick the knife further under and use a fast motion to push it out.

If its your daily driver and it would really really really be an inconvenience not to have it running, I'll suggest you do it over the weekend or just manage the hassle of the current P0638 till it really gets unbearable then you can proceed.

I've opened all of mine and I only managed to damage one. While cleaning it, I broke the white line on the electrical rail under the silver covering.

And truth be told I was only able to get one to work ok by cleaning it and it didn't last for too long before the issue resurfaced so it'll only buy you a little more time before you need to replace it. (Though that time I also used penetrating oil instead of contact cleaner so that might be what finally damaged it)

 

[NebulaStilo]

Well... I really can't help when it comes to that. I believe there would be a proper tool for removing it but I don't have that so I just take a knife OR a strong tiny flat screwdriver and force it out.

The metal always bends at the location where I pry and some of the plastic also chips away but.... that's life.

Its just a cover (I think) and its flexible so it can be bent back in place. So there is not much to fear.

Depending on how you pry it you might need to apply a lot of force to lift it off.

I usually look for a point at the outer edge, lift it, stick the knife further under and use a fast motion to push it out.

If its your daily driver and it would really really really be an inconvenience not to have it running, I'll suggest you do it over the weekend or just manage the hassle of the current P0638 till it really gets unbearable then you can proceed.

I've opened all of mine and I only managed to damage one. While cleaning it, I broke the white line on the electrical rail under the silver covering.

And truth be told I was only able to get one to work ok by cleaning it and it didn't last for too long before the issue resurfaced so it'll only buy you a little more time before you need to replace it. (Though that time I also used penetrating oil instead of contact cleaner so that might be what finally damaged it)

Think I'll just keep going until it gets unbearable.

Right now it's just not pulling as good as it used to but can live with that.

Maybe the weekend I'll take it off and give it a clean and keep you posted.

Mean time clutch is more important because it's slipping

 

[NebulaStilo]

Well... I really can't help when it comes to that. I believe there would be a proper tool for removing it but I don't have that so I just take a knife OR a strong tiny flat screwdriver and force it out.

The metal always bends at the location where I pry and some of the plastic also chips away but.... that's life.

Its just a cover (I think) and its flexible so it can be bent back in place. So there is not much to fear.

Depending on how you pry it you might need to apply a lot of force to lift it off.

I usually look for a point at the outer edge, lift it, stick the knife further under and use a fast motion to push it out.

If its your daily driver and it would really really really be an inconvenience not to have it running, I'll suggest you do it over the weekend or just manage the hassle of the current P0638 till it really gets unbearable then you can proceed.

I've opened all of mine and I only managed to damage one. While cleaning it, I broke the white line on the electrical rail under the silver covering.

And truth be told I was only able to get one to work ok by cleaning it and it didn't last for too long before the issue resurfaced so it'll only buy you a little more time before you need to replace it. (Though that time I also used penetrating oil instead of contact cleaner so that might be what finally damaged it)

Hi

Also tell me,can a slipping clutch also add to fact that my car is really down on power but she revs fine.

Also I herd it can also cause a surge in acceleration due to excessive wear.

Is that true?

 

[aijosh]

Sure. A slipping clutch would cause you to "loose power" in the actual sense of it.
But the clutch rarely fails so it should be the last place to look when you have power issues.

Also I think if the clutch is failing you'll definitely know.
How does the pedal feel? Anything weird?

Also try this:

.1 Start the engine and engage the emergency brake.
.2 Depress the clutch pedal.
.3 Shift into second or third gear and rev the engine to about 2500 rpm.
.4 Slowly release the clutch pedal.
.5 As the clutch engages the flywheel and pressure plate, the engine should stall. If the engine doesn't stall, then the clutch is slipping.

Still minor slipping shouldn't bother you.

A clutch job isn't something you want to do yourself unless you have good arms or are a weight lifter + a surgeon at the same time.

You would quickly realize, the bell housing is a pain to remove and put back unless its something you do regularly. Plus you might wear out some stuck bolts if you don't get them loose in the first few attempts or have the skill to loosen stuck bolts.

I've had to change my release bearing once and I wouldn't want to ever do another job that requires me getting into the assembly again.

If you are trying to get to the clutch because of the P0638 error then its a No No. Just change the throttle body first. I can bet its what your issue is.

 

[NebulaStilo]

Sure. A slipping clutch would cause you to "loose power" in the actual sense of it.
But the clutch rarely fails so it should be the last place to look when you have power issues.

Also I think if the clutch is failing you'll definitely know.
How does the pedal feel? Anything weird?

Also try this:

.1 Start the engine and engage the emergency brake.
.2 Depress the clutch pedal.
.3 Shift into second or third gear and rev the engine to about 2500 rpm.
.4 Slowly release the clutch pedal.
.5 As the clutch engages the flywheel and pressure plate, the engine should stall. If the engine doesn't stall, then the clutch is slipping.

Still minor slipping shouldn't bother you.

A clutch job isn't something you want to do yourself unless you have good arms or are a weight lifter + a surgeon at the same time.

You would quickly realize, the bell housing is a pain to remove and put back unless its something you do regularly. Plus you might wear out some stuck bolts if you don't get them loose in the first few attempts or have the skill to loosen stuck bolts.

I've had to change my release bearing once and I wouldn't want to ever do another job that requires me getting into the assembly again.

If you are trying to get to the clutch because of the P0638 error then its a No No. Just change the throttle body first. I can bet its what your issue is.

Sorry I meant to state that it is a problem besides p0638 lol.

My clutch is slipping because in higher gears around 3rd and up if I try to accelerate her past around 3000 rpm then she just revs as if the clutch pedal is pressed down. Therefore I cannot pick up high speeds and in low gears she revs high but her power output to wheels does not match.

There is some free play on the pedal and it does feel stiffer.

The clutch releases slowly too. I can't pop her even on gravel road. I have this one piece of gravel road I sometimes drive on at work and I tried to see if she will pop from stand still. She doesn't pop at all.

This is all seperate to p0638. I am aware I need to look at my potentiometer cleaning and in mean time shopping around for a throttle body(which honestly i cannot afford)?
I drive low revs and avoid traffic as much as possible.

 

[aijosh]

Oh. Ok. Something is definitely wrong down there in that department :devil:

Sounds like a worn out clutch. You should be able to get people that can cheaply fill in the pads. But its better to just get new ones or used ones. Its not a job you want to redo. Unless you have excess spare time and energy at your disposal

 

[NebulaStilo]

Oh. Ok. Something is definitely wrong down there in that department :devil:

Sounds like a worn out clutch. You should be able to get people that can cheaply fill in the pads. But its better to just get new ones or used ones. Its not a job you want to redo. Unless you have excess spare time and energy at your disposal

No definately not a job for me.

Im going to buy a brand new clutch kit.

Also my dad is a mechanic by trade and he has extensive experience in engines so I'll let him do it.

I was first under impression I need engine rebuild because all checked out i.e. o2 sensors and all the parts that could be affecting performance was replaced like o2 sensors,air filter,fuel filter,fuel pump etc so my next step was engine rebuild. My dad kept telling me the car doesn't need a engine rebuild,its something around the engine like a sensor or something that's affecting. That time I was getting no codes. Now I'm getting the p0638 and my dad like see,told you its something else??

Compression test was done and that was all ok.

But I definately need to replace clutch first,I can live with the bad throttle body and a heavy fuel consumption but I can't live with a bad clutch that will leave me stranded??

 

[NebulaStilo]

Oh. Ok. Something is definitely wrong down there in that department :devil:

Sounds like a worn out clutch. You should be able to get people that can cheaply fill in the pads. But its better to just get new ones or used ones. Its not a job you want to redo. Unless you have excess spare time and energy at your disposal

Hi there
Hope you well.

So I went into limp mode twice in one day,lucky me lol.

So twice I got p1687 along with p0638.

Definately throttle body I assume?

 

[NebulaStilo]

Oh. Ok. Something is definitely wrong down there in that department :devil:

Sounds like a worn out clutch. You should be able to get people that can cheaply fill in the pads. But its better to just get new ones or used ones. Its not a job you want to redo. Unless you have excess spare time and energy at your disposal

Hi

Update:

Removed potentiometer. Cleaned the tips and track that had some sort buildup on it. Not much though.

Doesn't seem to idle better.

Done a relearn like i saw on this group.

Car does respond to the pedal so it was put back properly.
Will feel it when I go to work.

Hopefully it is a little better?