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Followup To
Question -
Hi,
I have a 1995 Chrysler Cirrus with about 100,000 miles on it. Yesterday the vehicle started and hesitated and then died right outside of the driveway. The vehicle was restarted and then returned to the driveway. I came home from work and attempted to start the vehicle. The vehicle will turn over w/o a problem. I used some starting fluid to see if this would case the vehicle to a least fire and help to see if there was a fuel problem. The vehicle would just barely start but run exceptionally rough. I pulled the upper timing belt inspection cover and the timing belt appears to be intact and is turning normally. (The belt was changed about 3000 miles ago.) Next I attempted to obtain codes using the on-off-on-off-on method. The interesting thing I discovered at this point was that the check engine light was not coming on at all. I next pulled the instument cluster and tested the bulb by placing it in another functioning socket and the bulb appears to be fine. After this step I inspected all the fuses in the power module under the hood as well as the fuses on the left side of the dash. Any ideas? Bad computer?
Appreciate your help.
Answer -
Hi Robert,
I would begin by verifying that you are getting power to the PCM. With the ignition key on check whether you get voltage to pin 20 and then to pin 46 (those are on separate PCM plugs).
If not, then let me know. If you do get both those voltages let me know.
Either the PCM isn't getting voltage, the PCM is bad, or the data bus wire that provides the signal to the check engine (mil) light is bad, and we have to check this out step by step.
Roland
Thanks for the quick reply Roland,
I checked pin 20 and 46 on the separate PCM plugs with the key on the "on" position; both have voltage. Pin 20 was 11.7 volts and pin 46 was 11.9 volts. The battery is 12.1 (low because of cranking and no recharge).
Thanks and let me know the next step...
Robert
AnswerHi Robert,
Some further thoughts on the mil. That light is one of about 3 gauges and a dozen lights on the cluster who depend upon getting a digital data feed from the body control module, and it (as well as the coolant temp, cruise engaged, and low voltage warning bulb) specifically need a feed from the PCM to the body module, all of the data coming on the twisted pair of wires connecting all three devices (violet/brown, white/dark blue).
So although you can't start and drive the car, if the charging warning light bulb will still function when you turn the key to run, then the data path from the PCM to the body module and on to the cluster must be o.k. (The data for the mil would come from the powertrain controller as would that for the charging system, so if the charging light goes on it must mean that the mil light is either not having a signal sent out by the PCM or it is not getting the signal from the bus receiver that is associated with the cluster (implying a bad cluster bus or bad wiring to the bulb). So if you can look at the circuit board and verify the traces that power the bulb are o.k. it would seem to mean that the cluster data receiver is bad or it is not being reliably fed that data from the PCM output about the mil. Because the engine won't start, I guess I would favor your theory of a bad PCM.
I am stretching my competency to the limit with this one.
So do give me some feedback about how this gets resolved.
But do charge up the battery, nonetheless.
Roland
Hi Robert,
There is a 16-pin plug under the dash near the fuse box that is the data link connector. With the key off, and the PCM plugs disconnected make sure that the pink/light blue wire at pin 7 is not grounded. Similarly check the light blue wire at pin 6. Then check for continuity from pin 7 of the data link connector to pin 65 of the pcm plug. Then check continuity from pin 6 of the link connector to pin 75 of the pcm. If all those check out, then the voltage is getting to the PCM to run it, and the data link wiring from the PCM to the dash is o.k. Maybe one of the internal dash trace connectors to the bulb socket is bad? You also might want to charge the battery before buying anything, just to make certain. I don't know how much it will cost to get a used or new PCM so I'm a little leary about suggesting you get another one. The tests in my trouble shooting manual also have you run thru a whole series of tests of voltage supplies to the various sensors, but I don't think that is relevant if you can't get a check engine light to go on when you first turn the ignition to run (it should stay on for 3 seconds, as a test).
Roland
