Saturday, June 28, 2014

1998 Chevy Cavalier Z24 2.4L LD9 PCM Fuel Pump Relay Wiring Diagram







1998 Chevy Cavalier Z24 2.4L LD9 PCM Fuel Pump Relay Wiring Diagram Schematic.
Notes On Testing Fuel System Circuit To Check Wiring, Find Bad Wiring Or Shorts, Bad Fuel Pump Relay, And PCM Signals On 1998 Chevy Cavalier Z24 2.4L LD9 With 3rd Party After Market Vehicle Key Fob Required Security System Spliced In Up And Behind Drivers Side Lower Dash.

Plastic Key Fob On Key Chain Required To Be Present To Start Car. If The Plastic Key Fob Is Present The Fuel Pump Will Initialize For 2 Seconds Before Cranking. If The Gas Peddle Is Pushed Down To Wide Open Throttle On Power On And Crank That Forces Clear Flood Mode Resulting In A Starter Crank With No Start Condition PCM Will Reinitialize The Fuel Pump For 2 Seconds When Cranking Stops. Attempting To Start Normally After A Forced Clear Flood Mode No Start Will Start The Vehicle Normally.

If The Plastic Key Fob On The Key Chain Is Not Present The Fuel Pump Will Not Initialize On Power On Before Crank Like It Does If The Plastic Key Fob Is Present. When You Attempt To Crank With No Key Fob Present The Starter And The Fuel Pump Do Not Initialize. Cranking Does Not Initialize The Starter And Cranking Does Not Initialize The Fuel Pump. If Clear Flood Mode Is Used The Starter Does Not Initialize, And The Fuel Pump Does Not Re Initialize.

Notes: If Clear Flood Mode Is Used With Key Fob Present And Vehicle Starts Check Injectors For Leaking Injectors, A Bad Injector Seal.

I am confident that I have a bad electrical connection, bad ground or a fuel presure regulator control problem, leaking injectors, or injector seal issues.

When I apply power from battery I can pump until I disconnect.

Have you checked the fuel pump relay?
Did the car stop running because of spark?
Are you cranking to get fuel past the 2 seconds?

While cranking the engine,make a second pin of the relay is getting 12 volts coming from the Powertrain Control Module. This should be the Dark Green/White wire.

If the circuits are good then at the fuel pump relay jumper the 12 volt supply wire to the Gray wire and see if the fuel pump runs.

If the pump still does not come on then check the Gray wire from the relay to the tank and see if the wire is broken.

If there is power on the Gray wire at the tank but the pump does not run then verify the ground to the fuel pump is good and replace the fuel pump.

Can you help me with specifict locations and what kind of power to check on specific wires. I am working against time.

I am very appreciative of your quick response. I will loose some good day light soon.


The fuel pump grounds at G304, which is also the ground for most of the lighting, so if they are all working probably not a ground issue. Maybe the computer is losing supply? Check the green/white wire from the pcm to make sure you the pcm is dropping signal.

Also is did the check engine light come on? Does the security or anti theft light stay on while cranking?

Ok good stuff we might be getting close. The car does have lighting problems. We had to jump from one Sid to the other to get a light to work and day time lights flicker unless lights are turned on.

Where is G304.At the left front of the passenger compartment.

I thought I had a defective pump because I seen power at the pump. But may not have taken the time to see the power disappear after 2 sec. Which does not give it enough time to get fuel up on a newly changed fuel pump.

Definitely try the relearn i gave you, this could be the issue. The problem is that if it is anti theft it will probably need new passlock sensor to fix correctly. At this point I do not think the fuel pump is the issue. If you have power there and the ground is good then the pump should run shortly. If it does not then the pump is bad, that's where we need a fuel pressure guage. Every time you cycle the pump it should run shortly. I feel pretty confident your issue is not in the pump. I will be on again tomorrow some time as I am home with an injury, so let me know.

Ok but here is my issue before I put the tank back in.

Should it not pump fluid.

I just checked with the switch in the run position I get 2sec of power then in the crank I get power till I let off then no power on the gray and solid black which I was told from pump tech Suport is the source for the pump.

When I connect why can't I get fund to pump. If I put 12 on the gray and black I get fluid in less than 2sec.

I just ran another test. Battery a little low. Only getting 7 to 10 volts for two seconds then 5 volts when cranking. So I hooked up the boat battery that I have been using to apply 12 volts to the pump directly as a jumper to the existing in car battery and got the same result.


ps the "theft system" light does not go off after 10 min. As the procedure indicates??

When the ignition switch is turned to the ON position, the PCM energizes the fuel pump relay for 2 seconds allowing the fuel pump to pressurize the fuel system. If the PCM does not receive any ignition reference pulses (engine cranking or running) within 2 seconds , the PCM de-energizes the fuel pump relay; this causes the fuel pump to stop. Yes the gray wire is the power, but if you are losing ignition reference pulses then it shuts off. You are going to have to check the cam and crank signals next. You will need a scanner to check for these signals.


When I apply 12 volts from a boat battery to the Gary and Blk wire I can hear the pump and get instant fuel out of the output.

When I monitor the voltage at the conectors that connects to the pump. In the on position I get between 5 and 8 volts. Then it shuts off like I think it should. As we continue the normal process and turn the key to crank I get the gray and the black to show me the same 5 to 8 volts as long as I am cranking. Which leads me to belieive I may have a bad ground. Could it be that 8 volts is not enogh to power the pump.

A piece of info that I have not shared with you from the past that when you said something about light issues, is that a past just answer mechanic helped me repair a front head light by jumping a wire from the good one to the one that would not work because it was a easier solon that finding a common problem with a junction box under the battery??????

Is it possible that I am looking for a bad ground.
Is their a historical spot I should look at that would be common to light and fuel pump?

The easiest thing to do at this point would be to run a new ground wire at the gray wire at the pump, there has been some problems with these plugs. You have to have 12 v at the pump. If you don't then there is a problem. How many volts are in the battery? This is the voltage that you should be getting at the pump. This system is :

The pcm commands the fuel pump relay on then the relay pulls in and energizes the gray wire to the injectors and the fuel pump. At this point you should get battery voltage at the pump for 2 seconds or while cranking. If you have this scenario then the ground or plug would have to be the culprit. Run a new ground if you have this and it should run.

I have less than 200 ohm resistance from connector at pump to battery.

So I now must look to the B+ side to see where I am loosing power.

Can you please get me the schematic for this circuit and the connector locations?


splice s121 is In the engine harness, front of the engine, approximately 27 cm (11 in) from C100

It is one of two connectors and to be specific the B+. side of the equation. Under the dash board or the one by the tank.

run a external ground from the battery to black at tank that would have and proved the ground to prove not to be the problem.
I then needed and did start checking the B+ points coming from battery to the tank at all of the connection points until I found my voltage drop from 12

About the relay :
While cranking the engine,make a second pin of the relay is getting 12 volts coming from the Powertrain Control Module. This should be the Dark Green/White wire.

If the circuits are good then at the fuel pump relay jumper the 12 volt supply wire to the Gray wire and see if the fuel pump runs.

If the pump still does not come on then check the Gray wire from the relay to the tank and see if the wire is broken.

If there is power on the Gray wire at the tank but the pump does not run then verify the ground to the fuel pump is good and replace the fuel pump.

This test would have shown us if you were losing power, but in your response you said you checked the relay, which I assumed you did my test, so then we moved on to other possibilities, like grounds and connections.

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