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Here's my experience with code 543 and ways to diagnose (according to the service manual) and figure out whats wrong. After searching this out, no one seems to know what the deal with this is so perhaps this will help someone, sometime.

I just got done putting in a new motor, HCI upgrade, and fuel pump. I've drove it about 5 times and about 125 miles. On my way home last time, it was driving fine. Then all of a sudden it started to run crappy like it was missing, really rough and kinda sputtery. I look at my wideband O2 and it's reading between 15-18. I was also datalogging with the TwEECer and had the laptop on and monitoring. LAMBSE (what the EEC is trying to get the A/F ratio to be at) responded and was about 10 and the stock 02's reported lean. It just so happened that I had another tune already programmed was a open loop all the time setup, so I switched it over fearing that the stock O2's had gone crazy and I could force a richer A/F ratio. Car went to open loop, but WB still said 15-16 (sometimes to 18, mainly 15-16) even with LAMBSE at 13ish. I know that the tune, while in open loop, can get the A/F ratio close to LAMBSE as I've drove for a while like this. I nervously drove it home about 10 more minutes, ready to pull it over at any sec. I was very concerned about my stud mounted rockers loosening as I've had troubles with this.

Get home and pull codes, run a KOEO. KOEO gives you 2 sets of codes. The first set is KOEO codes and the second set is continous memory codes. KOEO's first set was 111, then the continous memory codes had a 542 and 543. The 542 could have been set by my jumpering the fuel pump test in the DLC (data link connector, the connector that you use to enter self test mode (KOEO, KOER)) to run the pump non-stop to check the fuel pressure.

I'm in the middle of diagnosing this, I'll update when/if I figure out what the problem is.

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The EEC monitors the fuel pump power circuit. Power for the fuel pump comes from the battery, through a fuse, then to the CCRM. A relay in the CCRM is grounded by the EEC when it wants the pump to run. It can also be grounded in the DLC. The output of the relay goes to the inertia switch then to the pump. The output of the relay also goes to the EEC (pin 8) to monitor the voltage that the pump is receiving. This is how the EEC knows that there is a problem. If it's grounding the relay to turn on the pump, it expects 12V on pin 8. If it isn't always 12V when it's grounding the relay, then it knows there is a problem. Apparently code 543 gets set if the voltage drops, say if the relay is bad.

First off, there is a difference between a KOEO code 543 and a continous memory 543. KOEO first:

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Diagnostic Trouble Code (DTC) 543/524 indicates a fuel pump secondary circuit failure between the B(+) supply and the FPM connection to the power-to-pump circuit.

Possible causes:
No Starts:

-- Open circuit between the B(+) supply and the FPM connection to the power-to-pump circuit.

-- Fuel pump relay contacts always open.

Engine Starts:

-- Left/Front HO2S short to power

-- Damaged Powertrain Control Module (PCM).

** Does engine start?

NO = fix open in circuit or replace CCRM. RERUN test.
YES = continue

CHECK FRONT/LEFT HO2S FOR SHORT TO POWER

NOTE:
Due to the internal circuitry of the PCM, a Left/Front HO2S signal short to power could produce a DTC 542/543.


* Key off.

* Disconnect left or front HO2S.

* Measure resistance between HO2S signal pin and KEY POWER pin at the HO2S connector.

** Is resistance greater than 10,000 ohms?


NO = replace the O2 sensor. RERUN test.
YES = continue

CHECK HO2S CIRCUIT FOR SHORT TO POWER

* Key off.

* Left or Front HO2S disconnected.

* Disconnect Powertrain Control Module (PCM). Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary. Leave PCM disconnected.

* Key on.

* Measure voltage between the HO2S signal at the HO2S vehicle harness connector and chassis ground.

** Is voltage less than 1.0 volt?


YES = replace ECM, reconnect the O2. RERUN test.
NO = fix short circuit, reconnect the ECM and O2. RERUN test.
END


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Continous memory 543

** Also a continous memory code 556/557?

YES = skip ahead to section after next YES/NO quesions
NO = continue

A Continuous Memory DTC 524/543, without the presence of a Continuous Memory DTC 556/557, indicates that during vehicle operation, one of the following has occurred :

-- Open in the B(+) circuit between B(+) and the fuel pump relay.

-- Fuel pump relay contacts opened.

-- Open in the power-to-pump circuit from the CCRM/LFP relay to the FPM splice.

-- Left/Front HO2S circuit short to power.


* Start engine.

* Check for engine stall/stumble while performing the following (also, if possible, listen for fuel pump turning off):

-- Shake, wiggle, bend the fuel pump relay B(+) circuit to the CCRM/LFP relay.

-- Lightly tap the CCRM/LFP relay (to simulate road shock).

-- Shake, wiggle, bend the power-to-pump circuit from the CCRM/LFP relay to the FPM splice.

* Key off.

* Inspect the CCRM/LFP relay connector and B(+) connector terminal for corrosion, damaged pins, etc.

** Is fault indicated/found?

YES = ISOLATE fault and SERVICE as necessary. CLEAR Continuous Memory DTC. RERUN test.
NO = Under certain conditions, a Continuous Memory DTC 524/543 may have been set without a Continuous Memory DTC 556/557, even though a fault has occurred in the fuel pump primary circuit. continue

A Continuous Memory DTC 556/557 indicates a fuel pump primary circuit failure has occurred during vehicle operation. Possible causes are:

-- Open VPWR in the CCRM.

-- Open coil in fuel pump relay.

-- Open in fuel pump circuit (PCM Pin 22).

* Start engine.

* Check for engine stall/stumble while performing the following (also, if possible, listen for fuel pump turning off):

-- Shake, wiggle, bend the EEC-IV vehicle harness fuel pump circuit (Pin 22) between the PCM and the CCRM.

-- Lightly tap the CCRM to simulate road shock.

* Key off.

* Inspect the PCM connector and the fuel pump relay connectors for corrosion, damaged pins, etc.

** Is fault indicated/found?

YES = ISOLATE fault and SERVICE as necessary. CLEAR Continuous Memory DTC. RERUN test.
NO = continue

CHECK LEFT/FRONT HO2S CIRCUIT FOR SHORT TO POWER

NOTE:
Due to the internal circuitry of the PCM, an intermittent left/front HO2S signal short to power could produce a Continuous Memory DTC 542 or 524/543.


* Key off.

* Install breakout box, if applicable.

* Breakout box installed, PCM disconnected.

* Connect a test lamp between the left/front HO2S test (pin 43) and test pin 40 at the breakout box.

* Key on, engine off.

* Observe test lamp for an indication of a fault while performing the following (the light will turn on bright when a fault is detected):

-- Shake, wiggle, bend the left/front HO2S circuit from the HO2S sensor to the PCM.

-- Lightly tap the HO2S sensor (to simulate road shock).

** Is fault indicated?

YES = ISOLATE fault and SERVICE as necessary. CLEAR Continuous Memory DTC. RERUN test.
NO = take to dealer for complicated analysis (sorry)

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A breakout box is a connector that plugs into the harness where the EEC plugs in. It provides pins so that you can probe the wires with a meter. Probing the pins in the harness can ruin them, so be careful as I'd bet no one has a breakout box except dealers. (the insertion of the meter's test probe can expand the connectors in the harness connector and then cause them not to make good contact with the pins in the EEC connector).

If this helps someone, let me know!

Rick
 

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so by PCM do they imply the thing by the cooling reservoir?

and is there an english version available to us not-so-technical-mumbo-jumbo-savvy folks?
 

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Discussion Starter #3
ECM = PCM = powertrain control module (computer)
HO2S = heated oxygen sensor
CCRM = constant control relay module (thing by the cooling reservoir) (houses fuel pump relay)
DLC = data link connector (plug in engine compartment used to enter self test mode)
DTC = code from self test
VPWR = vehicle power (CCRM pins 12 and 24)
LFP = low speed fuel pump (our cars only have a low speed)
FPM = fuel pump monitor (circuit from output of fuel pump relay to the ECM pin 8 to monitor the voltage)
B(+) = +12V battery power (fuel pump relay = CCRM pin 11)

If you have any other specific questions, feel free to ask.

Rick
 

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Sweet, so that code appeared after I ran through the water (flooded) and ruined my 02s. They got wet on the inside and outside (submerged) since they hang down so low with the LTs. I didn't know there was a relationship between bad 02s (172 & 176) and that code. Good stuff, I think I'll print that out.
 
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