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CAN bus problem?

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chapmro
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chapmro

CAN bus problem?

Post by chapmro » Mon Apr 08, 2019 10:03 am

Hello all,
I've been having a problem for a few weeks with my 2004 XC70 that has me stumped. Ideas?

Symptoms:
While driving on the highway, 80 degree day, AC on, first the cruise control stops working. A few minutes later the gauges all go dead except fuel, AC stops working. Car continues to run, except a little slow to respond to pushing the accelerator pedal, so I go to destination (100 mi). After stopping, the car won’t start for a little while (cranks, won’t catch. I re-seat the ECM, and wait about 1 hour (engine cools). The car cranks, but with the message “reduced engine performance”, and the following codes, read with the iCarSoft Volvo tool.

ECM-6620 (engine cooling fan module)
ECM-9530 (accelerator pedal PWM signal)
ECM-9540 (accelerator pedal PWM signal)
No other modules have codes

and the AC compressor is failing to engage (clutch doesn’t turn). I can drive the car. On one occasion for about 1 minute it did not respond to the accelerator pedal at all.

Already tried:
I replaced the accelerator pedal and engine cooling fan & module . No change. Codes return immediately upon clearing them. I sent the ECM and CEM off to Xemodex. Both passed testing as fine, but they thought there was enough chance that it was an overheating ECM that they cloned my ECM into one of their upgraded ones. I re-installed the two modules. No change in symptoms: Same codes, AC compressor not coming on. I looked at the datastream coming from the analog and PWM signals from the accelerator pedal ,and the analog voltage changes appropriately and the engine responds to the pedal, perhaps a little slowly, hard to tell. The PWM signal is stuck at 0%.

I’ve looked at the wiring diagram to try to find something these symptoms have in common, some place all the wires involved go, but can’t come up with anything. Ideas?

Thanks very much.



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RickHaleParker
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Re: CAN bus problem?

Post by RickHaleParker » Mon Apr 08, 2019 10:25 am

chapmro wrote: ↑
Mon Apr 08, 2019 10:03 am
The PWM signal is stuck at 0%.
1. Contact resistance or oxidation in the terminals between the ECM and the accelerator pedal position sensor.
2. Open-circuit or short-circuit to ground in the signal cable .
3. Open-circuit in the power supply (12V) for the accelerator pedal position sensor

I recall one electronic accelerator pedal that keep cutting out. The firewall had cut through the wire insulation and shorted out the signal cable. Re-insulationed the wire and all was well.


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chapmro
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chapmro

Re: CAN bus problem?

Post by chapmro » Mon Apr 08, 2019 1:34 pm

So, it turns out fuse #8 in the engine compartment had blown -- replacing this fixed everything for a few minutes (AC works, cruise works, no errors in ECM). However, after about 5 minutes of driving I lost the gauges again, and connecting the iCarSoft diagnostic tool reveals that nothing on the high-speed CAN bus can be talked to (ECM, TCM, BCM, maybe a couple of others) -- they cannot be found by the tool, cannot be queried -- this is how it behaved when the problem first manifested itself, and it has done it before on other occasions, always in hot weather. The only error in the CEM is "faulty communication" with the TCM. I turned the car off for 30 minutes, cranked it back, and the high-speed stuff has all reappeared. The only errors in those modules are "faulty communication with CEM". The errors can be cleared and the car runs fine (in park, no time to drive it again). My thoughts now are: connectors between ECM and high-speed CAN bus, or noise on the CAN bus, possibly overheating of the ECM and TCM -- can't verify that cool air is getting to it via the little pipe under the radiator and power steering reservoirs, or that the fan for the ECM/TCM box is working.



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abscate

Re: CAN bus problem?

Post by abscate » Mon Apr 08, 2019 4:00 pm

The 2004 CEM is known for overheating so google up the heat sink options, which have also been discussed here in this Forum.

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chapmro
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chapmro

Re: CAN bus problem?

Post by chapmro » Mon Apr 08, 2019 4:19 pm

Yes, that's why I sent the CEM to Xemodex and they sent me back one with beefed up heat sinks. So that's not the problem.



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Re: CAN bus problem?

Post by jimmy57 » Mon Apr 08, 2019 6:03 pm

Have you a tool to get ECM and TCM out? You could see what happens if you remove and use contact cleaner and then give them a WD-40 bath and put it back together. If that gives temporary relief then you need to do the drag test with a terminal crimped to a wire and probe the females in CM bases. You might be able to use a slender pick and push the terminals sides inward and see if the drag is noticeable and get that to work. If it's connections anyway.



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