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Chrysler Repair/'99 Grand Cherokee: code 1686, 1687


QUESTION: Starts and runs fine. Cluster and gauges function for about ten seconds, then dims and gauges quit. Headlights, front wipers, turn signals,hazard flashers and electric windows are inoperative. Front signal lights and indicators in cluster stay on dim, even after ignition switch is turned off. Sometimes the blower fan motor also runs with key off.

Disconnected gray connector from body module, cluster, gauges, turn signals and hazard flashers work normal. Still no headlights, wipers or electric windows.

Installed new BCM. Still have same problems.

ANSWER: Hi Randy,
Unfortunately I don't have a manual for Jeeps earlier than '06, and that year it doesn't even have a bcm! I wonder, based upon items that stay "on" even with the key "off", whether there might be short/open in the ignition switch. I wish I had a manual with the wiring diagrams but without it I just would be guessing. If you can find a factory service manual for it on eBay that would be the best place to start. It should be less than $20 and you search for "'99 Jeep Grand. Cherokee service manual".

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

QUESTION: Ignition switch was the first part that was replaced. The vehicle has a BCM and replaced it with a new one from Dodge.

Unable to communicate with BCM. Codes in the ECM are PO1686 and PO1687.

Those two codes refer to a problem of digital communication between the Powertrain Control Module and the Sentry Key Immobilizer Module (1686) and between the Powertrain Control Module and the Instrument Cluster (1687). The action taken of removing a plug from the BCM may have caused one or both of those codes. You would do well to disconnect the battery for a few seconds, then touch the two battery wires together (having removed both clamps from the battery), then reconnect the clamps to the battery. Then drive the vehicle and see if the same codes are still present.
If they are then I would find the communication bus wires (which are distinguished by being a pair of wires twisted around each other for their entire length) at the plugs for the PCM, the cluster, the BCM, and SKIM module and with the use of an ohmmeter or continuity tester then check that all the pins of the disconnected plugs that carry those wires are connected to one another (using the wire colors to identify the pin connections to verify continuity. Try gently flexing the wires while checking for continuity to detect a loose connection at each of the pins.
If the connections prove out, then I believe that it would be prudent to find a good shop which can use a diagnostic readout box to determine if the problem is the PCM, the cluster, or the SKIM module. It is too expensive to buy a module without proof that you have a bad one.
I don't have the wiring diagrams but you can ID the twisted wires to check, There should one such pair of twisted wires at each module.
Please read the PS below and respond to it.

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Roland Finston


Free fast answer to your repair question about a Chrysler/Dodge/Plymouth car, minivan, SUV, or truck. Problems with electronically controlled engines and transmissions as well as body wiring problems are my specialty. This free troubleshoot advice forum helps you diagnose faults, minimize repair costs or do-it-yourself.

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