fuel monitoring cicuit help

[Mic_]

Hello all,


1994 Explorer 138K on the clock.

I continuousdly get the KOEO code of 543.

Had CM of 543 but erased it.
So I am tracing a monitoring wire to the pcm.

Fuel pump runs and I have no issues. buT I am trying to locate were the DG/Y wire goes from the distribution to the PCM.

Where is the PCM and what is the routing from the distribution block?

ANy place in particular subjective to corrosion on this wire?

 

[MrShorty]

PCM is located behind the passenger kick panel, just in front of the passenger door, below the glove box.

 

[Mic_]

MrShorty,

Many thanks. Since the distribution box is also on the same side, is it safe to say the harness is routed tru the firewall there by the passengers' side ?

I am still getting a 543 KOEO code, that to me says the monitoring wire to the PCM is bad.


Some new info. I metered from pin 8 on the PCM connector back to the relay terminal and I get continuity. This same DG/Y splices to the inertia switch and powers the pump.
I am getting power to the pump, but the pcm is NOT seeing the power.
What gives? PCM going bad?

I ran a engine running test after warm up, and I still get a 543 code in KOER or in the KOEO (prior to seperator pulse).

 

[MrShorty]

Haven't ever had to deal with this specific problem. One thing with many of these kinds of circuits is the computer isn't so much looking for +12V as it is looking for a change in state as the pump is turned on then off during the KOEO test. I could be wrong, but I'm wondering if this code could also be set if the relay had been bypassed.

I checked the pinpoint test for a '95 (assuming the '94 is the same), and one interesting possibility they list for a KOEO 543 is a short to power in the left HO2S heater circuit.

 

[Mic_]

Haven't ever had to deal with this specific problem. One thing with many of these kinds of circuits is the computer isn't so much looking for +12V as it is looking for a change in state as the pump is turned on then off during the KOEO test. I could be wrong, but I'm wondering if this code could also be set if the relay had been bypassed.

I checked the pinpoint test for a '95 (assuming the '94 is the same), and one interesting possibility they list for a KOEO 543 is a short to power in the left HO2S heater circuit.

Change of state makes sense, rather than looking for the presence of +12volts.

With a DVM, should I reference that wire at pin 8 of the pcm to ground as I cycle the key (as if I was starting) to check that it is changing?

WHat is a "left HO2S heater circuit" ?.

If the fuel pump relay was bypassed, then only the powertrain relay controls the pump? At start up I listen for the pump, and it runs for a few seconds then stops, before I crank it.

You know I decided to just to check for codes, (not having the MIL light on) because I was under the hood doing a belt and a tensioner.

This one has got me stumped a bit.

 

[MrShorty]

"HO2S" stands for Heated Oxygen (O2) Sensor.

"With a DVM, should I reference that wire at pin 8 of the pcm to ground as I cycle the key (as if I was starting) to check that it is changing?" -- Sounds good to me.

 

[Mic_]

"HO2S" stands for Heated Oxygen (O2) Sensor.

"With a DVM, should I reference that wire at pin 8 of the pcm to ground as I cycle the key (as if I was starting) to check that it is changing?" -- Sounds good to me.

Sound like good info.

SOrry been busy with school, but I will ring it out and look at the O2 sensors for a short or crushed wire.

 

[Mic_]

For those that need closure....

Replacing the PCM cured my 'permanant' fault code and my poor idle.

 

[shamaal]

Super, thanks for the followup. I'll add it to the database.