Testing for Switched Power at the C4 J17 FP relay
06-03-2014, 12:32 PM
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Testing for Switched Power at the C4 J17 FP relay
These photos relate to testing to see if the issue with your C4 not starting is a broken ignition switch that is resulting in no switched power to the J17 fuel pump relay.
The J17 fuel pump relay trigger side has switched power coming in on pin 28/15 (i.e. from the No. 15 switched power bus to pin 28 in the FP relay base). The AAN ECU will not energize the FP relay until it is happy that the G28 Engine Speed sensor is sending a signal that tells the ECU that the engine is spinning at more than 13 RPM. When the ECU gets that signal it takes the switched power through the J17, to ground, through ECU pin T55/3.
This diagram shows the basic wiring and pin numbers. Note Pin 28/15 is the switched power into the FP relay.
Your AAN might not be starting because the battery is not strong enough to spin the engine to 13 RPM or because the ignition switch is failed and there is no switched power to the FP relay at pin 28/15 OR because the FP relay is broken. The next few photos just show you how to test for switched 12V at the FP relay.
Here is the J17 FP relay in its natural C4 habitat:
Here is the FP relay base showing the various female pins in the base, corresponding to the male pins on the J17 FP relay.
Here is one example test set up. I had a male-male jumper wire that I've had since 1984 when I had issues with my 1980 Mk1 Jetta fuel pump relay. I just added a shielded female spade connector to one male pin so I could stick the multimeter probe in there easier. The other male end was plugged into FP base pin 28. With the multimeter set to 12V DC and the (+) probe in the female spade connector end and the (-) probe grounded to a near-by bracket (not a bolt on the Bus bar), I switched the ignition to run. Got 11.5 V which is okay with the engine off. That was just to prove a point. I don't have *THAT* issue (but I still have my hot start problem which has now graduated to a cold start problem)
For a B3/B4 S2/RS2, the procedure would be similar, except the FP relay base pin that you would probe would be what appears to be 45/46 (Anybody with a photo of the relay base under the 208 FP relay in the S2/RS2 fuse/relay box?)
The J17 fuel pump relay trigger side has switched power coming in on pin 28/15 (i.e. from the No. 15 switched power bus to pin 28 in the FP relay base). The AAN ECU will not energize the FP relay until it is happy that the G28 Engine Speed sensor is sending a signal that tells the ECU that the engine is spinning at more than 13 RPM. When the ECU gets that signal it takes the switched power through the J17, to ground, through ECU pin T55/3.
This diagram shows the basic wiring and pin numbers. Note Pin 28/15 is the switched power into the FP relay.
Your AAN might not be starting because the battery is not strong enough to spin the engine to 13 RPM or because the ignition switch is failed and there is no switched power to the FP relay at pin 28/15 OR because the FP relay is broken. The next few photos just show you how to test for switched 12V at the FP relay.
Here is the J17 FP relay in its natural C4 habitat:
Here is the FP relay base showing the various female pins in the base, corresponding to the male pins on the J17 FP relay.
Here is one example test set up. I had a male-male jumper wire that I've had since 1984 when I had issues with my 1980 Mk1 Jetta fuel pump relay. I just added a shielded female spade connector to one male pin so I could stick the multimeter probe in there easier. The other male end was plugged into FP base pin 28. With the multimeter set to 12V DC and the (+) probe in the female spade connector end and the (-) probe grounded to a near-by bracket (not a bolt on the Bus bar), I switched the ignition to run. Got 11.5 V which is okay with the engine off. That was just to prove a point. I don't have *THAT* issue (but I still have my hot start problem which has now graduated to a cold start problem)
For a B3/B4 S2/RS2, the procedure would be similar, except the FP relay base pin that you would probe would be what appears to be 45/46 (Anybody with a photo of the relay base under the 208 FP relay in the S2/RS2 fuse/relay box?)
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UrS4boy
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11-06-2014 06:46 AM