No power to injectors or O2S in PDC - where to start looking?

My 1999 XJ won't start. The motor turns over but never fires and there are no issues with the starter, ignition, lighting, etc. After several hours of going through all the fuses and relays, it looks like they are all fine. I have found that I'm not getting power to fuse 21 and 24 in the PDM.



After tracking down what they do in a 99, it looks like these control the injectors and O2S heaters which would explain why it cranks but doesn't start. I verified the fuses are intact with a multimeter and that there is no current going through the location.

Where do I start looking next?

The ASD relay supplies power to numerous sub systems, ignition coil, O2 sensor heaters, injectors, fuse 21 and fuse 24 and more.

The ASD relay won't (stay) closed unless the PCM has a pulse signal from the CPS during cranking or when the engine is running.

Most likely cause of the ASD relay not closing is a bad CPS. But a sensor short in the 5 volt supply circuit for numerous sensors can also cause the PCM not to close the ASD relay. It is also possible it may be wiring issue in the ASD relay circuit, but less likely than the CPS or a sensor short (in my experiences).

One of the indicators of a sensor short is often the PCM shuts down power to the gauges.

Start by testing the Crankshaft Position Sensor.

Thanks for the help - CPS is showing infinite resistance between B & C. New MOPAR sensor ordered.

Check fuse 11 in the JB. It's power to the ASD relay control coil.

It also powers the TCM, PCM, and FP relay.



Here's a newer version of the PDC. Discard that other one.

Thanks for the help. The CPS was shot but the rig fired right up after I replaced it. BleepinJeep has a pretty good tutorial on the process of replacing it for anyone in need.