UrS4boy

<center><img src="http://pictureposter.audiworld.com/15624/j17functionandimportance.jpg"></center><p>
I knew that the ECU controlled the fuel pump (FP) relay (J17)(PN 4D0 951 253) (located under the driver's side (LHD) knee bolster, right end of relay panel) and that the ECU would not engage the J17 until it had a signal from the cam position sensor (G40) during start-up and then the crank position sensor (G4) during running. However, the FP relay does more than that.

From the above diagram, it can be seen that the ECU to signal to the FP relay comes from Pin 3/55 of the ECU as a brown wire with a yellow stripe, i.e. a switched ground. This pulls power from the No. 15 switched power terminal under the drivers side knee bolster. With current allowed to run from 15 to ground (via the ECU), the relay's electromagnets engage two contacts which then pull power off the unswitched (always hot) 30 terminal. This allows current to flow from the 30 power line to the J17 relay power outlet terminals, 87A and 87F. Terminal 87A energizes the N75 wastegate frequency valve, the five injectors (which get their duty cycle control from the ECU), the idle stablization valve (N71) and the emissions carbon cannister frequency valve (N80). Terminal 87F energizes the G6 fuel pump (via a green wire to Fuse No. 17 and then a green wire with yellow stripe to the FP) and the G39 O2 sensor via a black wire to a 12 Amp circuit breaker located under the passenger side (right side) kick panel.

As a result, some running and/or stalling problems could be related to a bad signal between the ECU and the J17 FP relay or the J17 itself. Simply jumping the FP from 30 to 87F will not prove anything because all the other devices, including the injectors will not be powered.

Update: April 4/09: 4D0 951 253 which was the 208 relay is now superceded by 4D0 951 253B, the 372 relay. KATE's verbiage is:

"contact close relay for fuel pump
relay location/code no.: 6/372
to be used for code no.: 208"

<a href="https://forums.audiworld.com/s4s6/msgs/126842.phtml">Link to G40 Cam Position Sensor Info</a>

<a href="https://forums.audiworld.com/s4s6/msgs/116988.phtml">Link to G4 Crank Position Sensor Info</a>

HTH somebody.

Bill the Cat

30 is not switched - Jumping the 2 large contacts energizes the fuel pump - key on or not.

UrS4boy

Thanks. I didn't think it was (but wasn't sure). I will edit the text.

UrS4boy

the car start as a FP relay test. Output terminals 87F/DTI and 87A also need to be jumped and powered as well. Easier to test the FP relay by replacing it with a known-to-be-good FP relay.

quantumrallysport

Ahh, but this may be a good way to get the car home if the CPS fails....

Jump 87F, 87F/DTI and 87A and drive home???

Idahospud

I would guess not. From what I've read, the ecu needs to get info from the cps for timing and ignition. I'm not a mechanic, but I wouldn't try it. It seems to be cheap and easy enough to replace the cps and fp relay to make sure their good. ..

UrS4boy

Wow. Way to drag the cat in, litterally, and punnily too.

Anyway, for more J17 Fuel Pump Relay as it relates to the G40 Cam position sensor and the G4 crank position sensor and the G28 engine speed sensor, click on the appropriate labels in this diagram (linked below) for more info.

http://members.shaw.ca/speedtek/UrS%...ice%20Map.html