PCM and it’s wiring

[Garrett]

Hey everyone, hope you’re all having a great Saturday.

Got a quick question here, and it may sound ridiculous, BUT, I have tried just doing the typical google search for this with not a whole lot of information I could find, and everyone who has helped me with struggles so far have all nailed it on the head, so why not throw it here! :silly:

Let’s say you have a wire harness that is fed directly to the PCM, this particular harness feeds all oxygen sensors, we’ll say it’s about an 8ft wiring harness. If at any point these wires may get HOT, as in too close to exhaust, or too close to engine, would it cause the PCM itself to “heat up”, and go into default settings without using the actual sensors themselves? But let’s say the wires aren’t melted, broken, or shorted, just getting really really hot at certain points to where if anymore heat had hit those wires, it would indeed melt. Are PCM’s smarter than they appear, where if it senses something like that, it would default and protect itself?

Thanks in advance for the info!

Topic

[Mike]

The PCM would not heat up in that situation.

Heat affects wires by increasing their resistance, which can affect the amount of current/amperage that can pass thru them. The PCM looks at the circuits to make sure things look as they should, and generates circuit codes if it sees a problem. I’ve never seen a circuit code generated in real life due to hot wires but in theory, it could happen. In reality, hot wires don’t normally affect the readings of sensors because there is extremely low current passing thru them, and current flow (amperage) is what high resistance in a wire causes a restriction of. Another thing too keep in mind is that oxygen sensor wires are expected/designed to be substantially heated by being near exhaust components, so there is a lot of heat tolerance built into them.

[Garrett]

That was exactly the kind of answer I was hoping to get. Thank you!

[EricTheCarGuy]

+1 the heat would’t be transferred to the PCM. Or maybe I should say it’s not likely any amount of heat that would be damaging to the PCM would make it that far. Computers speak in the language of voltage. Low system voltage is more damaging than anything when it comes to PCM’s. I hope that answers your question.

[Author]

Replies