U0121, U0151, U0155 Codes after cab-off repair. - Ford Powerstroke Diesel Forum
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Old 05-17-2014, 07:36 PM
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U0121, U0151, U0155 Codes after cab-off repair.

This truck just got some major work done at a Ford dealer. New fuel system (complete fuel system, fuel cooler, lp pump, scrubbed fuel tank, etc), oil cooler, radiator, and other odds and ends. It had the cab off for this. It was running great for a week, and yesterday, my instrument cluster stopped working while on the highway. Even my dashdaq quit reading data. The traction control light came on (tcs disabled). The a/c control panel (fancy king ranch one) appeared to work, but the compressor was not actually working. The instrument cluster started working sporadically, but the data display was still haywire. Tcs is still not functional, The airbag system says it is not working, and I have an intermittent wrench icon when all this happened.

That was yesterday, and it was working this morning just fine for a few miles. Then more of the same. I kept driving it, and the various failures would come and go. Then I started losing power, and I'm not sure, but I think it was because of a loss of signal from the throttle petal. It started running normally again minus the cab electrics, so I got it home.

Those codes in the title are from yesterday, I didn't scan it again when I limped it home today because I was in a rush. I just switched the kids, car seats, wife and stuff into my wife's perfectly functional (minus a flaky oil cooler) 6.0l and went off down the road again. I am betting there will be some new module communication codes whrn I recheck it tomorrow.

Obviously, some wire bundle is pinched, or a harness plug is loose. Does anyone know of a single failure point where all these power and data wires come together? I think it has to do with one of the the big harness plugs below the coolant bottle. I checked them this morning before trying to drive the truck, and they all seemed tight. I also checked the pcm plugs, and they looked and felt right.

Anyone experienced something similar? I think I'm going to have to take it back to the dealership and have them fiddle with it, since I am pretty sure it is because of the cab removal process.
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Old 05-18-2014, 05:57 PM
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There are 3 connectors by the left front spring tower that need disconnected for the cab to come off. 2 big connectors have slide levers and can be very hard to unplug and reseat if they are dirty. Check there first. The only other 2 are on the other side by the PCM/Air filter. Those are the main engine harness connectors. The PCM connector is easily broken if the locking lever is forced off
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Old 05-19-2014, 08:08 PM
Emergency Services


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Thanks, Matt

Those plugs on the spring tower seem like the problem to me. If the PCM plug was loose, I don't think it would run at all. I think I figured out the problem with my accelerator petal. When the ABS module would lose connection momentarily, it seemed to think I was skidding, and it would dethrottle the engine. I finally got over that when I was driving it today by turning off the TCS.

Anyhow, a closer inspection of the plugs by the spring tower still look ok to me, so I decided to run the truck back to the dealer and have them track it down. If they accidentally caused this problem, they should fix it. If they somehow accidentally caused a new ongoing problem, I want a paper trail about it.
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Old 05-30-2014, 05:42 PM
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I had something similar happen on a truck I worked on. One of the 2 huge connectors on the shock tower was superglued together by godknowswho. I took a mental note of it. When I put the truck back together it had intermittent u-codes. Obviously I was blamed for getting the "hot potatoe, you touched it last". Had to spend a few hours tracing wires and installing random extra connectors to bypass the unreplacable connector.
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