300M will not crank

My 2000 300M suddenly decided not to crank over. I have a wiring diagram
and have troubleshoot the problem to the point that I know that the battery
and starter are good. Everything in the starter relay circuit checks out
with the exception of the powertrain control module. It appears that the
PCM is preventing the starter relay from operating. This seems like it
could be a failure of the PCM, or perhaps the PCM seeing something wrong
from some sensor and preventing start.

Does anyone have any suggestions for futrher testing? I do not have an
analyzer I can't check for usefull info from the OBD II.

Does anyone have experience with a similar problem?

Thanks!

 

Maybe it thinks you're in gear (ie not park or neutral) ?

 

Thanks, but I do not think that the problem is the transmission interlock.
My wiring diagram indicates that this interlock would prevent voltage from
the battery from reaching the coil of the start relay. In fact I do have
voltage there when the ignition switch is in start and the transmission is
in park. The PCM interupts the part of the circuit from the relay coil to
ground. That is why I think that the problem is the PCM or one of the
sensors.

 

Which would mean a bad transmission range sensor - this problem does
occur. The PCM is looking for the shifter to be in park or neutral
before it enables the starter relay.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')

 

The PCM has to see a signal from the *tranny* *range* *sensor* saying
that it is in park or neutral before it will issue that ground to the
starter relay coil to enable it (so that when the start signal comes
from the start contact of the ignition switch to the other side of the
relay coil, the relay hits the starter).

MoPar Man was right: The PCM thinks the tranny is not in park or neutral
and so is not grounding the starter relay coil. Probably the tranny
range sensor has a problem.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')

 

OK Thanks.

Is there any way I can check the sensor without dismantling the
transmission, or should I just give up and have it towed?

 

Why don't you run the stick shift up and down the range a few times,
or try starting it in neutral (or find the ground connection on the
starter relay and temporarily hard-wire it to ground?).

 

This may sound too simple, and you've probably checked it, but you'll
want to make sure that all of the wiring on the transmission is properly
plugged in. I've never looked at a 300M, but I've noticed that the wire
to the sensor comes unplugged sometimes on the front of a Dodge Caravan
transmission, causing exactly the symptom you're describing.

 

to add to this. check and clean all the connections on the power post under
the red cap and at the ground post at the shock tower i see this all the
time and there is a revised wiring kit for the positive battery cable but it
must be looked up under 1998 or99