Dreaded trans. Failsafe prog.

[andrewwynn]

Originally Posted by Corellian Corvette

If you have a Power Probe, you can feed power to each line on the O2 sensor circuit. You have the TCM removed, and the 02 sensors removed then no reason not to feed power to each wire and see which one trips the breaker.

Or you could simply get a test light and see which wire provides the ground to turn the light on?

You have to cut them apart to do that test.

If any wire is grounded they are all grounded through the common splice.

[Corellian Corvette]

Maybe I missed it but all 4 share common power?

[Oldmactech]

I’m not certain but the red/white stripe wire that gets power from the f4 fuse provides power to the heater circuit on each of 4 O2’s. But at the F4 fuse box there is only one wire that runs out of the EBox into a wire bundle wrapped with waterproofing through a finned plastic conduit then breaks into 4 red/ws lines and 4 black rounds for the 4 O2’s.

If the short is somehow inside the wrapped wire bundle or the conduit will be beyond my meager skill and physical reach to replace a wire(s). Sure hoping the short is from the rear of the engine forward or I’m gonna have to send it out.

Been pouring over the Bentley electrical diagrams hoping there is some sort of relay or other fuse that makes it appear there is a short but so far nothing.


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[andrewwynn]

On my car, the split of the main feed is visible inside the ebox. That connector is a crimped connector and can/should be cut apart to determine where the fault lies.

As long as they are all connected you can't tell without visual tracing the entire wire where the short is

[Oldmactech]

I’ll look for that. Thanks.


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[Corellian Corvette]

So I totally believe all this but then how the HECK does the ECU know the voltage at each O2 sensor??

[andrewwynn]

The resistance of the sensor and ECM after very very high in relation to the wires going to/from the sensor such that the wires are negligible.

The O₂ sensor generates a voltage based on the relative O₂ content of the air inisde the exhaust and the reference sample of O₂ in the wire lead coming into the sensor outside the exhaust.

That voltage travels down the lead wires at nearly instantaneous speed: roughly 180,000 miles per hour or 1/3600 the speed of light. It's effectively inside the ECU electrically.

[andrewwynn]

The wires in question are not the sensor wires they are the heater power leads.

The heater power is always active when the key is on (and up to a few minutes after the key is off). The heaters are controlled with PWM control of their respective ground paths.

[Oldmactech]

I believe that is true so I’m only looking at the red/ws wires coming to the 4 wire connectors to the O2 leads. A little earlier you referenced a “main feed” that is a crimped connector? When looking for that will that be immediately emerging from the 5 fuse holder at fuse 4 or somewhere down stream?

Thanks.


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[andrewwynn]

I can't remember where that splice was but it should be close to the fuse. I thought you already identified it.

Where about seven wires are crimped together, two of which go to EGS, four to the O₂ heaters. That needs to be cut apart. If you cut through the crimp with a Dremel you can avoid having to try to strip the wires to reattach later. There might not be enough wire to do that without difficulty.

You cannot determine which of the wires is shorted when they are all connected.