Pin C on the Fuel pump relay requires what voltage from the ECM? 12 volts - 5 volts? My ECM pin A1 isn't driving the FP relay . Does the FP driver pin C need to be active all the time or just on startup?

Thank you!!

 

Pin "C" on the fuel pump relay is just the fuel pump relay control wire from pin "A1" of the ECM. The power source is pin "E" and is a orange wire coming from the battery through that 20 AMP in-line fuse. Pin "C" of the relay is activated by the ECM for 2 seconds when the key is first turned to the "ON" position. After that it is a tan/white wire from pin "B2" (fuel pump control) on the ECM to the fuel pump.

 

OK

My problem is that pin C on the relay is not receiving anything from A1 of the ECM.

I am trying to come up with a way to manaully activate pin C on the relay for the startup. I was considering a switch to send voltage to pin C before I turn the ignition key. If this works create my own circuit to do the 2 second feed of pin C on the relay to correct what the ECM is no longer doing.

Just trying to figure out if pin C requires 12 volts or another voltage.

 

Okay, here is a test that you can do. Take a test light and disconnect the fuel pump relay. Using the test light, probe pin "C" of the connector and have someone turn the key to the "ON" position and watch the light. If it comes on for two seconds, replace the relay and the ECM and wiring is good. If it doesn't come on, you either have a broken wire, short to ground, or a faulty ECM.

 

ok, A1 is not lighting up when I put the test light direct to A1 on the ECM. when I turn the key to the "run" position, the test light never lights up. Is it possible that this is the only ECM pin that would fail?

Ok, so if I install a switch that would feed 12 volts from the orange wire to the green/white wire on the relay that should allow the fuel pump to run until the car Starts.

 

Actually running a 12volt source to pin "C" of the relay wouldn't help you at all. If you are so dead set in doing this, you need to jumper pins "A" & "E" at the relay connector or put a switch between the two wires and the pump will run continuosly until you pull the jumper or turn that switch off. This might be a good fix for a short period of time but it is not recommended as a permanent fix. You should fix what appears to be the problem from what you have said, the ECM.

 

First what is the vehicle problem? The fuel pump can be energized by running 12volts thru a 10 amp fuse to pin "G" on the ALDL connector. That bypasses the relay altogether. The ECM NEVER feeds the pump relay 12 volts, it provides a ground to the low side of the relay coil(the side of the relay coil that does not tie to 12 volts directly) to energize the relay coil and turn on the relay. Remember, the fuel pump has TWO power souces, the relay and the oil pressure sender switch. When the fuel pump relay fails the typical problem is you have to crank the engine several times before it will start. The sender requires 4psi oil pressure for the switch to close and it will run the pump on it's own. Y should be able to pull the fuel pump relay out completely when the car is running and it should continue to run if the sender sw is good. Never apply 12 volts to the ECM side of the relay directly or you will fry the quad driver in the ECM. Also, if you run 12v to "G" as soon as the relay turns on the pump will stop, the G is only a test point with the key off.

 

What is the problem with the car? The ECM grounds the low side of the relay(the side of the relay not tied to 12 v directly). With the car off Y can run 12 volts to "G" connector pin on the ALDL and fire up the pump, it's for test only. If the relay turns on it disconnects the test 12v from the pump. Remember, the are TWO voltage sources to the pump, the relay and the oil sender switch. A typical TG problem is hard starting if the fuel pump relay fails, you need to crank it several times until 4 psi of oil pressure closes a switch in the sender sending 12 volts to the pump. Y can pull the relay completely out when it is running and it should continue to run if the oil sender sw is good. Never apply 12 volts directly to the ECM side of the relay coil, you will destroy the quad driver in the ECM. Rarely if ever does the ECM fail that way unless someone screws up. Get back to me with more info.

 

I am having a problem with the car rough starting and error code 54. The car does start but after 30 seconds or more of cranking. I ran thru the trouble shooting flowchart and found that pin C on the relay is not receiving anything from A1 of the ECM. I also placed a test light on A1 on the ECM. The test light still does not come on. Therefore the ECM must be replaced.

I was trying to come up with a work around rather than replace the ECM.

 

Wrong move. Y will get nothing from A1 with a test light because it is an open collector transistor in part of a package called the quad driver. The ECM sends NO voltage, it grounds the low side of the relay coil. Y will generally see no voltage there because if the relay is pulled there is no voltage source, the coil of the relay passes voltage to A1 and when the car is turned on the A1 pin goes low to ground one side of the relay. If it does start and run Y can rule out the ECM temporarily. Could be low fuel pressure from a clogged filter, or possibly an EGR problem. Even if the driver in the ECM was bad it would take several cranks to get the car running but it would run just fine because the oil sender will send 12 volts to the pump. 50-75% of all ECM's returned to GM depot repair have nothing wrong with them, it's usually misdiagnosis. Sometimes the ECM will have a problem internally with PC board connections. Y can try tapping on the module when it's running and see if it stumbles or throws a code. Then it's most likely something internal to the unit.

 

Wrong move. Y will get nothing from A1 with a test light because it is an open collector transistor in part of a package called the quad driver.

When you say "Y", are you referring to pin "C" on the relay?


The ECM sends NO voltage, it grounds the low side of the relay coil. Y will generally see no voltage there because if the relay is pulled there is no voltage source, the coil of the relay passes voltage to A1 and when the car is turned on the A1 pin goes low to ground one side of the relay. If it does start and run Y can rule out the ECM temporarily.


The test light does not light on pin C with the relay plugged into the harness and the ignition key is in the run position. With the test light on A1 of the ECM, the relay plugged into the harness, and the ignition key in the run position, the test light never lights.


Could be low fuel pressure from a clogged filter, or possibly an EGR problem. Even if the driver in the ECM was bad it would take several cranks to get the car running but it would run just fine because the oil sender will send 12 volts to the pump.

It does take several cranks to get the car running and it runs just fine.

50-75% of all ECM's returned to GM depot repair have nothing wrong with them, it's usually misdiagnosis. Sometimes the ECM will have a problem internally with PC board connections. Y can try tapping on the module when it's running and see if it stumbles or throws a code. Then it's most likely something internal to the unit.Then it's most likely something internal to the unit.

The ECM otherwise is running fine.

 

Here is the trouble shooting chart for code 54.

Danno, I have outlined the section here that he used to check pin "A1". This is a part of the procedure for checking the ECM, wiring, and relay for faults. circuit 465 listed here is the pin "A1 at the ECM going to pin "C" of the relay.

Pdiminico, when he says "Y" he means the word "YOU"

 

part 2

 

TNX "T", I forgot the fuel pump relay is the only one that does get 12 from the ECM, all the other relays get grounded from the ECM. My apologies P, memory needs upgrading. Y should get 12 volts at A1, make sure Y have a good chassis ground, sometimes its tough with body corrosion etc.

 

Relax Danno, as long as it is just the memory that needs upgrading you'll be fine. A buddy of mine went for a pre-employment drug test and it came back positive for Viagra, rogaine, and Geritol.