Plymouth Repair/2001 Neon:


QUESTION: I have been experiencing an issue with my neo. The check engine light and air bag light both come on at the same time and "no bus" is being displayed on the odometer. Everything I can find on the Internet says this is a PCM issue. The car runs fine, no mechanical difficulties at this moment. The local auto shop deep a deep diagnosis scan and did not return positive codes. Now the brake light comes on and off when I take off or turn a curve like a wire is shorted. I just do not know what my next step would be. Replace the PCM? replace the instrument cluster? I have done a visual inspection of the wires and the harness but I do not see anything obvious.

ANSWER: Hi Thomas,
Absent a code of 0600 or 0601 I would not waste my money on a PCM.
The brake warning light probably is telling you that the level of brake fluid in the master cylinder is low, so check that out.
'No bus' may mean that there is either a bus wire disconnection or a cold solder joint at pin 2 of you your cluster, so remove that cluster and heat the point between the cluster socket and the circuit board at pin 2. The violet/yellow wire at pin 2 of the cluster is the bus communication wire and it is connected to pin 59 of the pcm, pin 2 of the data link connector under the dash where a diagnostic readout box connects, pin 21 of the air bag control module so you could use an ohm meter to test that the violet/yellow bus wire is connected between all those points as a possible fix as well for the 'no bus' message on the cluster.  That will probably reveal a problem that is causing most of these warnings. Start at pin 59 of the pcm plug and verify a connection to all the other points that I listed.
To remove the cluster you remove the trim on the post next to the window, remove the top cover above the cluster, remove the bezel that surrounds the cluster, remove the 4 screws that hold the cluster in place, and then pull rearward, then disconnect its plug. You can then access pin 2, its wire on the plug for checking that continuity to pin 59, and the solder joint at the pin 2 socket/circuit board connection.
Please 'rate' my answer (see below).

---------- FOLLOW-UP ----------

QUESTION: I have continuity on wire from pin 2 on cluster to pin 59 on the PCM. I also checked at the Data link and Air Bag Control module. Everything seems to have continuity. No cold solder at the connector to the cluster. Even the brake fluid is fine. Any other suggestions?

ANSWER: Hi Thomas,
With the ignition key "on" check for DC voltage on the violet/yellow wire at the data link connector. It should be less that 1.5V. Let me know if otherwise. If it is less then there is another test to run.

---------- FOLLOW-UP ----------

QUESTION: Checked with the key "on" there is less than 1 volt.

It may be that one of the bus modules is shorting to ground or the bus itself may be shorting to ground;
Now disconnect the - post of the battery. Measure the resistance to ground of the violet/yellow wire at the data link connector. Is the resistance to ground greater than 1,000 ohms. If not, then remove the bus modules one at a time to see if there is one that is causing the reading to be less than 1,000.  With all the modules disconnected is the resistance below 1,000 ohms? The modules are: the cluster, the pcm, the anti-lock brake controller, the sentry key immobilizer, the airbag control, rhe remote keyless entry module, and the left and right side impact airbag control modules.

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Roland Finston


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