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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 any codes

The AC compressor is failing to engage (dash light comes on, but clutch doesn’t turn, fan but not cold). I can drive the car. On one occasion for about 1 minute it did not respond to the accelerator pedal at all, but resumed on its own just as I was about to call the tow truck.

I replaced the accelerator pedal assembly 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, no cruise control. 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, but can’t come up with anything. Ideas?

Thanks very much.
 
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