Would a mechanic try to fix the wiring?

[briwayjones]

Here's the deal! My Explorer is constantly throwing PO600, PO800 codes. PCM communication errors. Which in turns also throws a PO174, lean bank condition because of the communication problems. So possible causes are a bad PCM and bad wiring. I suspect it is bad wiring. I say that because PCMs don't usually go bad that often and I've already had a bad wire from the PCM to the A/C which kept the A/C from working.

Now, is a run of the mill mechanic going to try and do much diagnosing on the wiring? I'm guessing that would be time consuming? Is there any half decent way to fix that wiring given the nature of the complexity of that wiring that a mechanic would try? Is or the mechanic just likely to say that it needs a whole new wiring harness? Which is out of the question.

I need to put it in for at least a couple thousand of mechanical work to string it along for a few more years. But there's no point in doing that if it would need a whole wiring harness.

 

[Mbrooks420]

All depends on the mechanic. Some audio shops also specialize in electrical trouble shooting, since the car stereo business took a dive.

 

[J_C]

I'm not sure I follow your cause and effect deduction that the PCM codes cause a P0174. I'd sooner suspect an intake manifold gasket leak.

Not all mechanics are equal in training or diagnostic procedure. You do not need an entire wiring harness to fix a PCM comm error, but whether the technician can trace the fault, some could and some would throw parts at it. Sometimes you can't even be sure if they're being honest with you and they sell you a marked up PCM but all they did was solder or secure a frayed or shorting out wire.

The point is there is no easy way to predict what a mechanic will do, only the possibility to figure out the true cause and then assess the cost effective ways to fix it right, or rig it to work in a non-OEM way that still works.

Some things you can try are making sure the battery is not excessively drained, that will definitely cause weird PCM errors. Also unplug and replug the two bulk wire connectors under the hood, one on the firewall and one probably on a bracket on the engine.

It could help if you track down the engine computer wiring diagrams for your model and engine. It "might" help to hook it up to a scanner capable of realtime data.

With a wiring diagram you can unplug the PCM, see what color wire goes where, and use a multimeter to check for continuity between both ends of the wire, and between either end and ground (if it's shorting out but shouldn't be grounded). If you have a connector with corroded pin(s), many can be pulled out and cleaned or a new connector pin crimped on. If the wire is damaged a new wire can be put in place of the damaged section of the old one.

That is not the type of thing a dealership would do. They are the most likely to want to replace an entire OEM *part #* with one they can order and install.

 

[Jim Faulkner]

J C has it. I would add that a lot of the smaller mechanic shops are not going to do a lot of electrical troubleshooting. Electrical issues suck - very hard to trace out and fix. According to engine-codes.com:

Intake air leaks
Faulty front heated oxygen sensor
Ignition misfiring
Faulty fuel injectors
Exhaust gas leaks
Incorrect fuel pressure
Lack of fuel Faulty
Mass Air Flow (MAF) sensor
Incorrect Positive Crankcase Ventilation (PCV) hose connection

Have you checked the air filter, and cleaned the MAF sensor?

 

[briwayjones]

I'm not sure I follow your cause and effect deduction that the PCM codes cause a P0174. I'd sooner suspect an intake manifold gasket leak.

I've dealt with lean bank faults before from various reasons. The P0174 only gets set when and at the same time as the P0800 and P0600. And since the PCM controls various engine functions I think it could easily cause that code.

 

[J_C]

I've dealt with lean bank faults before from various reasons. The P0174 only gets set when and at the same time as the P0800 and P0600.

Then how do you explain other people getting a 174 without the other two codes?

And since the PCM controls various engine functions I think it could easily cause that code.

I don't mean to stop you from troubleshooting this any way you want to, and maybe it doesn't matter because unmetered air getting in by itself wouldn't set the 600 and 800 codes so you can attack that angle and see if it makes your 174 go away.

 

[briwayjones]

Then how do you explain other people getting a 174 without the other two codes?

I'm not referring to P0174 codes in general. In this specific case the code only coincides with the P0600 and P0800 codes. It only appears at the same time, and only when those two codes are set. That is why it seems like in this case, with my car that there is some kind of PCM issue. That I believe is a wiring issue since I have already had one bad confirmed wire from the PCM.

 

[J_C]

In what way was the wire damaged, where? I'm trying to associate what might damage one and this other one also. I mean offroading or road debris I could see it getting one on the bottom of the vehicle but the further up it is, the less likely it seems unless a mouse/etc was chewing on them or the whole harness was against the exhaust manifold.

I'd hook it up to a scan tool to look at live running data.

If you had a mechanic find and fix that wire to the A/C, that seems like a good person to take it to, to try to get that fixed instead of a new harness set.

 

[briwayjones]

It was a wire to the A/C. I don't know exactly where or how the wire was damaged. The mechanic didn't say. He made a passing remark about mice chewing wires so I'm assuming it may have been mice. He didn't fix it by dealing with the wire in the harness. He bypassed it and ran a wire between A/C components to fix it. Maybe from one pressure switch to the other. I'm not entirely sure, I'm not super familiar with A/C systems. But that's what it looked like to me.

Say there was one or two bad wires in the harness from the PCM. What would be the easiest, most likely way to fix it? Disconnect that wire from the harness connector that connects to the PCM, connect a new one to the connector and run the new one to wherever it goes without even getting inside the harness? That's about the best way I can think of.

 

[Mbrooks420]

Easiest way to fix a damaged harness is to just splice in a new wire using solder and shrink wrap, or quality butt splice connectors that are watertight.

 

[J_C]

If you can pull enough of the damaged section of wire out of the harness bundle then just solder in a new segment and cover with heatshrink tubing. If you can't (reasonably) find the area, just know that a specific wire has a break then yes run a new piece of wire the whole length. If it is not encased in tubing and anywhere near a heat source, it would be better if it's silicone insulated.

If the whole bundle is in split loom tubing then you can probably get new wire stuffed in and just leave the old damaged wire in there unless it's shorting against another one, but this seems more like it would be a case of flex failure or heat damage to insulation than a mouse getting into a plastic loom.

The more tedious part is going to be figuring out which wire(s) if you don't see any sign of damage nor does a scanner data stream show anything. Keep in mind that a failure to communicate might not be the PCM or wire but the component on the other end of the wire, or the connector.

You might also consider setting out some mouse traps near the vehicle.