Tuesday, June 14, 2011

How to test ignition switch and transmission range sensor switch on 2003 Mercury Grand Marquis?

At the ignition switch verify the yellow wire has voltage at all times, the white/pink wire should have voltage with key in crank position......if only yellow wire has voltage replace ignition switch......If both are good check for voltage at white/pink wire at transmission range switch while key is in crank position, if no voltage but voltage at ignition switch replace wire........If there is voltage on white/pink at transmission range sensor check for votlage at red/light blue wire at transmission range sensor.....If white/pink has vltage but not red/light blue then transmission range sensor needs to be adjusted or replaced.........If all is good up to this point access starter relay wires......Black wire should have good ground if not run to new ground, yellow wire should have good voltage if not run new wire to yellow wire at ignition switch, and red/light blue wire should have voltage with key in crank position if not run new wire from relay to transmission range sensor......The yellow/light blue wire at the relay should have voltage with key in start position, if not replay relay...If it does have voltage but yellow/light blue wire doesnt have voltage starte replace wire between starter and relay. Here is a wire diagram to help,


Also other possibility for no start problem are as follows:---
Check for power and ground at the pcm. Check the EEC relay and fuses. Check the ground connection near the battery. If everything looks good it is probably a bad pcm.

The EEC relay should be near the fuel pump relay.



Check the powers and grounds according to the chart.

Clear view of the image:---

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Car no start:--