Symptoms:

I got a call the other day to troubleshoot a 2003 Grand Caravan. According to her, this vehicle suddenly quit 2 months ago and 2 mechanics saw it already. They replaced the battery and starter and still it won’t start. When I saw it, I hooked up my Autel generic scanner and there is no communication with the engine computer. When I tried turning the ignition key, the engine would not turn over.

Diagnostic to troubleshoot 2003 Grand Caravan:

A no communication problem on any vehicle usually indicates that one of the sensors (or wiring between sensor and ecm )is shorted to ground and dragging the BUS communication signal down to 0 volt.

The first thing I verified for the no computer communication is the dash panel. I turn the key on and the ecm engine light stayed on all the time. Talking to the owner, she confirmed that ecm light has been on all the time for the last 12 months she was driving it until it quit.

Looking at the 2003 Grand Caravan wiring diagram, I verified if the computer is really working or not. Tracing the 5 volt reference voltage supplied by the computer, it showed the tps wiring colors and one of the 3 tps sensor wire is the reference wire. Measuring this reference wire voltage with key on engine off (koeo), it showed zero volt reading. The same reading results were given when testing the map sensor reference wire. This shows the ecm is not working.

Tips on to troubleshoot 2003 Grand Caravan for No Start:

With key off, disconnect the tps and map sensor one at a time and watch the scanner if it will communicate. Sometimes, if the sensor itself is grounded, it will bring the engine computer back to life and communication restored.

The same technique could be used on the crank sensor which is grounded by the ecm. In most cases, a crank sensor failure will disrupt the engine communication. When disconnecting these sensors, cycle the ignition key to reset the ecm before checking the scanner for communication.

There is also a possibility that other modules are defective (shorted) too that can affect the ecm. You can disconnect them also and test the ecm if it will communicate. Finally, with ecm terminals disconnected, check all the ecm ground voltage readings and max reading should not exceed 0.250v. If all sensors and modules disconnected have no effect of the ecm communication with ground wires voltage reading OK, then definitely the ecm is up for replacement.

Thanks!