Hello,


I need help trying to figure out to fix CM Code 542. She starts right up, but after she warms up, her idle would drop with CEL flicking when it goes back to normal idle. It will do it here n there. But today she kept CEL lit, until I turned the vehicle off and restarted her, which then it cleared than relit on and off.


These are the following items I have replaced and have done since owning the vehicle for about a month. I am not original owner. I bought vehicle from a guy that gave up on her and left it in poor condition. I have gotten her back to full life only stumbling on this code 542. Anything would help please. Thanks.


i conducted and replaced the following:

oil change

Radiator flush

Replaced thermostat

New ECT sensor

New MAF sensor

New ICM

New TPS sensor

New exhaust system from Cat back.

New purge solenoid

new O2 sensor on driver side manifold area

New fuel filter

New spark plugs and wires

Placed Seafoam in fuel tank and Crankcase.

 

Welcome to the forum

542 - Fuel pump open, bad ground or always on - - Power / Fuel Pump Circuits

Computer can also use these codes but didn't
543 - Fuel pump monitor circuit shows no power - Power / Fuel Pump Circuits
556 - Fuel pump relay primary circuit fault - Power / Fuel Pump Circuits

So when you turn on the key do you hear the fuel pump run for 2 seconds and then shut off?
Thats what it should do, each time key is turned from off to on, it will only run 2 seconds, test for that

After startup fuel pump will be activated full time

You could have a failing computer from the description

 

RonD,

Thanks for the reply. yes the fuel pump turns over for 2 secs than turns off. The Innova code book stats it's a fuel pump secondary circuit fault. Any clue what that even means? Relay possibly?
Im getting only 1 code from both ODB1 reader and when I use jumper wire to read the CEL blinks. Both come up as 542. Haynes manual stats fuel pump circuit open; pcm to motor? But Innova it's a secondary circuit fault. So not sure where to start.

 

Secondary circuit is the fuel pump power and ground

Primary circuit is the fuel pump relay

The Computer is connected to fuel pump relay on pin 22, with key on pin 22 should show 12volts, that tells computer the Primary circuit is OK, if no 12v then code 556 would be set

When computer activates fuel pump relay, that's sends 12volts to the fuel pump, the computer should also get 12volts on pin 8, if not then code 542, secondary circuit fault

If fuel pump was not getting 12volts then engine would not run, it wouldn't run rough it just wouldn't run

You can test if pin 8 is working at inertia switch under glove box
Hookup volt meter to either wire on inertia switch, or if you unplug it use dark green wire
And ground the meter
Turn on the key and you should see 12volts for 2 seconds
THEN you should see 5 to 8 volts, thats from the computer's monitor circuit(pin 8), if lower than 5v then computer issue in that circuit

 

RonD,

Thanks bro your the man..! I will definitely check it out 1st thing tomorrow. Now if pin 8 is the problem, does that mean I have to replace the computer? Or would I have to replace the inertia switch?

 

Wouldn't be inertia switch issue

Could be corroded connection or failing wire from pin 8 to inertia switch

You can pull out computer and check connector for water intrusion or corrosion, and test OHMs between pin 8 wire and inertia switch wire

You can open the computer and check main board for any discoloration, look here: Ford EEC-IV

You can see the 3 Blue Capacitors, these can leak after 20+ years and cause odd issues, under $5 to repair, if you solder
Pictures here of that: Capacitor Repair: Ford A9L ECM « Moates Support

 

RonD,

Appreciate it bro... I will definitely give you an update when I finished my diagnosis.

 

Sounds good

One other thing to test, just thought of it
Start engine and let it idle, test voltage on battery, should be 13.5-14.5volts, remember it

Then test voltage at inertia switch, should be the same voltage, if its under 12volts then that may trigger code 542
The computer gets the 13.5-14.5 volts from its power wires and fuel pump should be getting that same voltage, if not then computer may set that code
The lower voltage would mean corroded wire from Fuel Pump relay in engine bay to inertia switch

 

RonD,

Okay so on 1st test I got 12v for 2 secs than reduced down to 6-8v but never went under that.
2nd test I turned ignition off and tried again see if I get same result. Well I got constant 12v and fuel pump didn't turn off, plus I can here lots of flickering in the fuse/relay panel area.
I swapped some relays around to see if it was only that, but no kept flickering and constant 12v.
I also here whisking noise from FPR area, but fuel pump is staying on constant with out me turning over engine to on.
I have to wait or play with on off until pump stops so I can start vehicle.
8pin seems to be fine if I got 1st reading above 5v n never dropped. But now pump constant on, with flickering noises in relay box area and whisking noise from FPR simultaneously. Any ideas?

 

My battery voltage is 14.5 - 14.8. While vehicle is running. Brand new battery too.

 

Battery voltage is OK

You said you have new fuel pump relay right?

Yes pin 8 should be OK

So now you will be looking at pin 22 athe fuel pump relay GROUND

You will need to check the OBD1 reader port in the engine bay

Look here: https://therangerstation.com/tech_library/OBD_I.shtml

2nd drawing shows the OBD plug with Fuel Pump slot labelled
This slot is connected to pin 22 on computer AND the fuel pump relay

A relay has a coil of wire around a metal core, when this coil of wire has 12v AND a ground it becomes a magnet and pulls the metal arm in the relay down to make an electrical connection

The Fuel Pump relay's coil get 12volts with key on, pin 22 on the computer is the ground, computer grounds pin 22 for 2 seconds then un-grounds it and waits for RPMs to go higher than 400 and will then ground pin 22 again and leave it grounded until key off or RPMs drop under 400

That slot in the OBD plug is a way to test if computer is grounding and ungrounding that pin 22 wire...................or if maybe this ground wire is shorted to ground in the harness somewhere
Could also be a problem inside computer with pin 22

So you can use a volt meter or test light on that slot and hooked to battery positive
The slot will have 12volts key on, thats the voltage passing thru the relays coil and how the computer "sees" if Primary fuel circuit is working, and it does "see" that because no code 556

Anyway, volt meter hooked to battery positive and that slot should show 0 volts, then key on it should show 12volt for 2 seconds then back to 0 volts, when computer grounds pin 22

 

RonD,

So I have cleaned all of the engine grounds I could find. Cleaned the inertia connector. I pulled all relays/fuses out of engine box and cleaned the connectors with electrical spray and wire brush, tugged all the wires and all tight too. As I placed each relay and fuse back to its correct spots I used steel wool and cleaned the relay/fuse prongs. I then turned over the key to on and fuel pump engaged and turned off within 2 secs. I did it again and test was Sat. I even left it in that position to see if any flickering noises, there was none. So I turned vehicle over she started right up, no hesitation.

I had to make sure this ain't no fluke. So I connected my odb1 reader and performed test with engine off. got no trouble codes. I disconnect it to do another test, same no codes. So I still wasnt convinced. I used my jumper wire, and sat in the car waiting for codes, all i got was 111 three times. So I'm assuming what ever I touched or cleaned helped out.
it's dark out now, so tomorrow in the AM, I will be going to test drive to see anything happens.
I appreciate all the great info, this was a learning experience here on electrical diagrams and checking. Very tidus work. But well satisfying. Thanks again bro. I'll let you know if anything triggers or happens after test drive.

And fuel relay still same, not new.

 

Good work

Yes, electrics is very tedious work

 

RonD,

So I took it for a test drive. Worked fine for about 45 mins. Then I I placed her back in drive way, she did it again. Flickering at fuse box/relay area, and CEL on an ran sluggish. Turn it off and placed ignition on engine off. Same thing flickering and pump constant on, never turns off. So i did the ground check as you said on the odb1 terminals. I got 12v. But when it starts to flicker it jumps all over between 0 - 11. So I'm assuming it's the computer. Well I disconnected the wires see very minor corrosion on pins, I'm going to clean them. But I also opened the computer up like you said. I did find all 3 capacitors leaking and one with snapped leg. So I will get a relative of mine that is a 2M technician and have him repair the board. Hopefully that was the culprit. I'll let you know in a week or so, after repairs are done.

 

Yes, the capacitors are the culprit

 

RonD,

Drove 150 miles on the truck, and zero issues. Definitely runs 10x's better, idles smoother, and fuel pump turns on and off as designed. To include no flickering noises in fuse/relay box. Those 3 capacitors was the culprit. Thanks for all the advice and help. Appreciate it.

 

Good work

Thanks for the update and the FIX