ECM Codes

[jdawg99]

I have a question about diagnostic codes on my '94 Explorer. Got five codes that came up: 326,332,335-egr related, 543-Fuel pump secondary circuit failure battery to control module, and 565-canister purge curcuit failure. The egr related items I will tackle separatly. Does anyone know what or where the fuel pump secondary circuit from the battery to PCM connection is? I am sure the canister purge circuit failure is due to excess fuel in my vapor canister(was told over filling gas tank can lead to this). My wife drives this vehicle regularly and need to get this problem fixed asap. I work out of town all week and have two and a half days a week to work on these problems that come up. Any info would be appreciated, Thanks.

 

[MrShorty]

I am sure the canister purge circuit failure is due to excess fuel in my vapor canister(was told over filling gas tank can lead to this).

Incorrect. The computer has no idea what is in the vapor canister or the tubing. 565 only refers to the integrity of the electrical circuit to the CANP solenoid. Usually either a full open or a short to ground in the circuit. It's a pretty basic DC circuit. Assuming it's a KOEO code (I have never seen it come up elsewhere), this should be pretty easy to pinpoint with a voltmeter and a wiring diagram. You may also find the output state test useful in diagnosing this circuit. You might review my notes on pulling EEC-IV codes thread in the EEC-IV forum to see how to run the output state test.

543: 1st question -- KOEO or CM or both? I can never remember which is "primary" and which is "secondary", but the PCM sees the fuel pump circuit in two parts: The part from the battery post to the fuel pump monitor circuit (pin 8??, need a wiring diagram to tell for sure) and then from the monitor circuit through the pump to ground. Your list suggests that 543 refers to the part between the battery and the PCM. If it's a KOEO code, it shouldn't be too difficult to track down with a wiring diagram and a voltmeter. If it's a CM code without an accompanying KOEO code, it suggests that the circuit fault is intermittent, which makes it a little harder to track down (because you have to look for the fault while the fault is present).

EGR codes: My code list indicates that a 335 can only be a KOEO and the others would be CM codes. SOP with EEC-IV codes is to resolve the KOEO codes first, so focus on the 335. Because KOEO codes are set while the engine isn't running, they almost have to be electrical in nature (which almost certainly rules out the EGR vavle itself). As frequently as the DPFE sensor seems to fail on these, I'd probably inspect the wiring between the PCM and the DPFE sensor and, if that checks out OK, replace the DPFE sensor.

 

[jdawg99]

Thanks for clearing that up for me. I will check out these things in the morning. My electrical diagram showed that the PCM power relay was connected to the canister purge solenoid. Maybe this is only due to the power distribution, these are all red wires that seem to be connected. But I will check all this out, Thanks for you advice.

 

[MrShorty]

My electrical diagram showed that the PCM power relay was connected to the canister purge solenoid. Maybe this is only due to the power distribution, these are all red wires that seem to be connected.

That is correct. Many of the engine management solenoids share a common power supply and the PCM acts as a ground side switch.