Technical Intermittent problem switching off GP

[Bartoosh]

Hi all,

The car in question is a Fiat Grande Punto 1.2. Recently it's experienced intermittent issues when shutting down. On the odd occasion the engine will not switch off immediately when the ignition is turned off. It can run on for up to 30 seconds before eventually switching off.

I tested the problem whilst running MES. The MES diagnostic report shows the car taking time to move the 'Ignition key position' parameter from "MAR" to "Stop" to "Blank" and 'Engine status' parameter from "MAR" to "Parking" to "Blank".

MES shows 1 error recorded by the Engine ECU:
U1706-87 – CAN network (NCM – NFR) – Missing message
Error in communication between engine control unit and ABS/VOC brake system control unit. Check CAN lines. The fault is present now. Take appropriate action to fix this sensor fault. Dashboard warning light was not activated for this fault.

By "Check CAN lines" does MES mean to check the wiring? If so, which wiring?

Thanks in advance.

 

[AnthonyH]

To understand CAN see the video below.



The CAN is basically two wires, down these two wires each module sends information. Each module is separate and there are over a dozen of them in the average car. For example a powertrain module, or a transmission control module.

Your error code is telling you that the ABS/VOC brake system control unit has a problem, and this is likely (but not certain) to be the cause of the engine run on.

Your CAN itself has no error, so you need to check the wiring between the CAN and your ABS/VOC. If the wiring is OK you'll need to repair or replace the ABS/VOC.

 

[GrandePunto PL]

Search for old threads like that. There was a case where main fuse/relay box corrosion caused such behavior.
Plus other things in the area, like ABS pump connector...

Then basics (fundamentals), main ground, ignition switch.
Body computer module as a last thing (also connections, corrosion, "cold solder" joints).

Ignition switch simplified diagram (starting): https://aftersales.fiat.com/elearnsections/main.aspx?nodeID=199001400&languageID=2&markID=1&modelID=199000000&valID=199000000&prodID=199000000&modelName=Fiat - 199 - Grande Punto&langDesc=English&sectionName=Impianto Elettrico&validityName=1.2 8v

More detailed schematic (there's more contacts inside): https://aftersales.fiat.com/elearns...nto Elettrico&validityName=1.2 8v&isExaminer=

 

[Bartoosh]

"Your CAN itself has no error, so you need to check the wiring between the CAN and your ABS/VOC. If the wiring is OK you'll need to repair or replace the ABS/VOC."

Thanks for the video. So if my understanding is correct the CAN lines are effectively wires connecting the various modules on the network.

When you say "check the wiring between the CAN and your ABS/VOC" do you mean check the CAN BUS wiring between the ECM and ABS/VOC?

Also, the video you shared mentions that a typical CAN has two 120 ohm terminator resistors at either end of the network to stabilise voltage and maintain signal integrity between ECU modules. Do these exist on the Grande Punto and, if so, where can I locate them?

I should say that no other errors are being reported. I checked CAN settings on MES and all modules are present and communicating. The ABS/VOC module itself shows no errors, the ABS light isn't on, and the brakes work fine. The only error being reported is by the ECM and this appears only when the vehicle struggles to switch off immediately. Judging by the diagnostic report, upon ignition off the vehicle is going through its shutdown procedures but the ECM isn't receiving a timely message from the ABS/VOC, resulting in a delay in shutdown.

 

[Bartoosh]

Search for old threads like that. There was a case where main fuse/relay box corrosion caused such behavior.
Plus other things in the area, like ABS pump connector...
View attachment 459639
Then basics (fundamentals), main ground, ignition switch.
Body computer module as a last thing (also connections, corrosion, "cold solder" joints).

Ignition switch simplified diagram (starting): https://aftersales.fiat.com/elearnsections/main.aspx?nodeID=199001400&languageID=2&markID=1&modelID=199000000&valID=199000000&prodID=199000000&modelName=Fiat - 199 - Grande Punto&langDesc=English&sectionName=Impianto Elettrico&validityName=1.2 8v

More detailed schematic (there's more contacts inside): https://aftersales.fiat.com/elearnsections/main.aspx?nodeID=199008233&languageID=2&markID=1&modelID=199000000&valID=199000000&prodID=199000000&modelName=Fiat - 199 - Grande Punto&langDesc=English&sectionName=Impianto Elettrico&validityName=1.2 8v&isExaminer=

Thanks for the detailed response and links. I neglected to mention earlier that I have already checked the fundamentals. The main grounds are fine. There is no corrosion in the fusebox and all fuses and relays are present and correct. I've visually checked the connectors on the ECM, ABS and BCM. There is no corrosion, bent pins, or water ingress. I also sourced another ignition switch but this made no difference.

As MES has suggested checking the CAN lines, this turned my attention towards wiring. However, as wiring is a minefield, I'd like to be clear which looms I should focus on. For example, there's wiring linking the ECM and ABS/VOC, wiring linking the ABS/VOC and ABS sensors, etc.

In addition, I would also like to rule out any other obvious candidates that I may have overlooked. For example, are there any tests that can conduct with a multimeter on the ECM and ABS/VOC connectors?

 

[AnthonyH]

Thanks for the video. So if my understanding is correct the CAN lines are effectively wires connecting the various modules on the network.

Yes. Imagine you have 20 modules in the car, now you have to connect each module to each other, so module 1 has 19 wires coming off it. Module 2 has 19 wires coming off it...and so on. So you would need literally hundreds of wires to do this. Or alternatively you use two CAN wires and have each module "talk" along them.

When you say "check the wiring between the CAN and your ABS/VOC" do you mean check the CAN BUS wiring between the ECM and ABS/VOC?

No, if there were something wrong with the CAN bus you're dashboard would be lit up like a Christmas tree. I mean find the ABS wiring and check that, with a bit of luck you've got a split wire and upon repair the problem will be solved.

Also, the video you shared mentions that a typical CAN has two 120 ohm terminator resistors at either end of the network to stabilise voltage and maintain signal integrity between ECU modules. Do these exist on the Grande Punto and, if so, where can I locate them?

Now this is getting tricky...I'm going to ping @PuntoHowTo who's often good at this kind of thing.

I should say that no other errors are being reported. I checked CAN settings on MES and all modules are present and communicating. The ABS/VOC module itself shows no errors, the ABS light isn't on, and the brakes work fine. The only error being reported is by the ECM and this appears only when the vehicle struggles to switch off immediately. Judging by the diagnostic report, upon ignition off the vehicle is going through its shutdown procedures but the ECM isn't receiving a timely message from the ABS/VOC, resulting in a delay in shutdown.

Its still probably pointing to an ABS problem, despite MES not recording a fault.

 

[Bartoosh]

Yes. Imagine you have 20 modules in the car, now you have to connect each module to each other, so module 1 has 19 wires coming off it. Module 2 has 19 wires coming off it...and so on. So you would need literally hundreds of wires to do this. Or alternatively you use two CAN wires and have each module "talk" along them.

Ok, got it. Removes the need for a multitude of wires and a central computer. Enables the modules to directly communicate on the network.

No, if there were something wrong with the CAN bus you're dashboard would be lit up like a Christmas tree. I mean find the ABS wiring and check that, with a bit of luck you've got a split wire and upon repair the problem will be solved.

Understood. This is where the fault code returned by MES frustrates. It suggests to "Check CAN lines" but it appears that I should focus on the ABS wiring rather than the CAN BUS. The fault code also states "Take appropriate action to fix this sensor fault". Is this another red herring or should I test the ABS sensors too?

Now this is getting tricky...I'm going to ping @PuntoHowTo who's often good at this kind of thing.

I'd appreciate that so I can rule out this possibility.

 

[AnthonyH]

Understood. This is where the fault code returned by MES frustrates. It suggests to "Check CAN lines" but it appears that I should focus on the ABS wiring rather than the CAN BUS. The fault code also states "Take appropriate action to fix this sensor fault". Is this another red herring or should I test the ABS sensors too?

You need to check the wiring and ABS sensor. I like the academic videos, so this one will give you a good idea of the theory involved and it shouldn't be too hard to find another that goes into taking the sensor off and checking it. The second half of the video goes a bit too technical.

 

[Bartoosh]

Off to make a cuppa and watch some videos.

 

[AnthonyH]

It occurs to me that you should clear this code and see if it comes back. It'd be best to check for error codes after the car engine runs on again, that'd be a smoking gun. Its possible that this stored error code is just some random legacy issue that isn't related to the current problem, and you don't want to remove the sensor if it isn't the problem, the sensor might just break for no good reason other than it was moved...

 

[Bartoosh]

It occurs to me that you should clear this code and see if it comes back. It'd be best to check for error codes after the car engine runs on again, that'd be a smoking gun. Its possible that this stored error code is just some random legacy issue that isn't related to the current problem, and you don't want to remove the sensor if it isn't the problem, the sensor might just break for no good reason other than it was moved...

Good thinking but I'm one step ahead of you there. I cleared the code and it returned the next time the engine ran on. I cleared the code again and when the car stopped normally, no error code. The following occasion that the engine ran on, the error reappeared. Whilst it ran on, I ran the diagnostics. Hence the error I posted says it's present rather than historic. I'm certain this error is linked to the symptoms.

As for messing with the sensors themselves, that'll be a last resort. For now I'm planning on focusing my investigation on checking terminals as well as connection issues at the ABS sensor plugs, wiring between the ABS sensor and the ABS pump, and the ABS module loom. Having trawled through other ABS threads on the forum these appear to be the most common issues.

 

[AnthonyH]

Good thinking but I'm one step ahead of you there. I cleared the code and it returned the next time the engine ran on. I cleared the code again and when the car stopped normally, no error code. The following occasion that the engine ran on, the error reappeared. Whilst it ran on, I ran the diagnostics. Hence the error I posted says it's present rather than historic. I'm certain this error is linked to the symptoms.

As for messing with the sensors themselves, that'll be a last resort. For now I'm planning on focusing my investigation on checking terminals as well as connection issues at the ABS sensor plugs, wiring between the ABS sensor and the ABS pump, and the ABS module loom. Having trawled through other ABS threads on the forum these appear to be the most common issues.

Sounds like a good plan! Let us know what you do, any issues/questions post a pic for the best responses.

 

[Bartoosh]

Quick update. I removed the front windscreen wipers followed by the scuttle panel to reveal the bulkhead area. It wasn't too bad in there but I gave the area a good clean to prevent future issues. The drainage tubes are clear so rainwater is able to escape but I may consider modifying these later to route water away from key parts like the alternator. I quickly ran out of daylight so I switched my focus to watching the CAN BUS Diagnosis video above before performing diagnostics. I checked for resistance on the CAN lines by probing pins 6 (+) and 14 (-) on the OBD2 port with a multimeter. The reading is 61.8 ohms, which I understand is a good result. This suggests that the main CAN lines on the BUS are fine (though there still could be a wiring issue local to a module). The ABS module is not reporting any errors in MES and I'm able to actuate the ABS Pump motor and drain/load valves. On the weekend, I'll take a closer look at the wiring around the ECM and ABS modules, in the bulkhead and between the ABS pump and sensors.

 

[AnthonyH]

Any updates?

 

[Bartoosh]

Nothing yet, unfortunately. I've got a feeling that the ground circuit for the ABS module is open. However, trawling through looms of wire looking for a fault is like looking for a needle in haystack, made all the more enjoyable by the recent cold snap.

 

[AnthonyH]

Nothing yet, unfortunately. I've got a feeling that the ground circuit for the ABS module is open. However, trawling through looms of wire looking for a fault is like looking for a needle in haystack, made all the more enjoyable by the recent cold snap.

I figured the wiring at the ABS module in the wheel arch would be faulty, i know the brake pad sensors are just useless and the wires get chewed through there, so i figured its either that or needs a new ABS sensor.

I haven't done as much as i'd like on my car, just too cold....but its heating up in a couple of days, hopefully spring is on its way then.