2001 XC70 Blowing Fuse#8 and Accelerator Cut Off with Brake

aronthemechanic2016 · Post by **aronthemechanic2016** » 10 Feb 2016, 20:59

Hello. We're having 2 major issues with a used XC70 we just purchased. The #8 fuse (AC Compressor/Accelerator Pedal Position Sensor) keeps blowing. It will blow when I crank the ignition and when I turn on the AC. The only way for the fuse not blowing is by slipping it in the fusebox while the car is idling. As soon as I turn on the AC, the fuse will blow. I think it's the AC compressor that is causing this issue, but why will the fuse blow when I start the engine with the AC off? Do I need to replace the compressor or clutch?
The second issue is with the accelerator pedal not responding when the brake pedal is applied. I can rev the engine above idle constantly, but as soon as I step on the brake pedal, the rpm drops to idle. With the brake pressed, the accelerator pedal does not respond no matter how hard I step on the gas. There seem to have no communication between the gas pedal and the engine. Could this be caused by the fuse#8 also? But the strange thing is, with or without the fuse# 8 blown, I can still accelerate the engine. The acceleration only cuts off when I step on the brake. Any ideas?

Post by **precopster** » 10 Feb 2016, 21:20

No accelerator with brake pressed is an ETM problem.

You need to break the A/C lead going into the small connector on the A/C clutch so you can place an ammeter in series with the A/C compressor.

If you have a clamp meter you can measure the current draw without breaking the wire.

Post by **abscate** » 11 Feb 2016, 05:31

Mike...isn't braking suppression of throttle normal ETM software? That's what they taught us in Skip Barber when we did heel and toe brake/throttle on modified cars.

I do think OP has an AC fault that is blowing the fuse

Post by **precopster** » 11 Feb 2016, 05:57

On my XC it depends on the ETM and firmware level of the ETM I'm testing.

My non turbo ETM car can be heel and toed all day long

There is a later firmware level that doesn't do this.

aronthemechanic2016 · Post by **aronthemechanic2016** » 11 Feb 2016, 12:55

Thank you for the responses. Regarding the ETM being the cause of the accelerator not working while brake is applied, I've read a faulty brake pedal position sensor can also cause the same symptom. Do you think this is a possibility? The car idles and runs smoothly (no surging, hunting, or bogging down). Besides the brake/throttle issue mentioned before, out of nowhere the car will loose accelerator pedal response while driving. I've been stranded on the side of the road 3 times already with engine smooth idling and no reaction from the accelerator pedal. After multiple restarts, it'll run again. Last week, my Indie removed the ETM and gave it a good cleaning. Even though it looked super clean, he cleaned it again with TB cleaner and brass wire brush on the plate and edges. If in the end the ETM is faulty, should I reprogram, replace the complete unit, or replace only the TPS. The ETM has a white sticker. I'll post some readings from the scanner a little later.
Regarding the AC compressor fuse, is there any way to disassemble the fuse box and trace the wire(s) to the offending component? There is a wire harness going out of the fuse box, and there seem to be a few pins that is related to fuse# 8. What components are on fuse# 8 circuit? Any links to diagrams we can refer to? Thanks again.

MarcM · Post by **MarcM** » 11 Feb 2016, 15:59

Isn't the white label ETM the bad one with the wiping contact position sensor issue?
Edit: RESCINDING THIS POST! Realized that both have the same issue potentially, just the yellow label may last a bit longer. The XemodeX and some other replace the strips with hall effect pickups. My error. Going back to sleep and minding my own business

Post by **abscate** » 11 Feb 2016, 18:35

The ETM fault isn't something that cleanng the visible part of the throttle body can fix - the problem is in the contact sensor inside the housing.

With 16 years and ??? Miles on the ETM it doesn't owe you anything - or more accurately it doesn't own the PO anything.

aronthemechanic2016 · Post by **aronthemechanic2016** » 11 Feb 2016, 20:09

Thanks to all that have responded. I cannot believe it! Persistence does pay off. Found out why fuse 8 was blowing. The grey wire going from fuse box harness to the ac compress coil connector was grounding. So we cut the grey wire at the harness, then installed a new fuse and everything seems to be fixed now. The fuse does not blow on start up or with the AC on (with the AC coil wire disconnected). The accelerator pedal now works with the brake pedal, and throttle response is more connected with no lag. I cannot explain why, but cutting this grey wire at the harness seem to fix all my problems. Now I need to know if I can connect a new wire directly from the fuse box to the AC coil? I'm getting 13 volts coming out of the grey wire from the harness. Can I connect 13 volts directly into the coil to make the ac work?

aronthemechanic2016 · Post by **aronthemechanic2016** » 11 Feb 2016, 20:12

BTW, the difference between the 2 TPS in the ETM is 0.5 degree. Is this a good way to tell that the ETM is still okay?

Post by **precopster** » 12 Feb 2016, 06:03

The 0.5 degrees is well within the 13 degrees allowed by factory when new (post 2006) software is fitted. I've fitted contactless TPS and found up to 1 degree difference.

It was old firmware that was less tolerant and put cars in limp home mode with the slightest deviation between sensor 1 & 2.

However the boards fail in so many different ways with internal faults ranging from boards that don't provide voltage to contact strips to processing faults that don't output one of the TPS signals.

Perhaps that A/C circuit fault and resultant accelerator pedal malfunction is a partly failing A/C coil with a lower than normal impedance. If you measure the resistance of the A/C coil what value do you get?