Diagnostic Test

WARNING: This page is about a different car, the 2005 Jeep Grand Cherokee. However, it is still accessible from the selected car via links, so may be relevant.

1) ACTIVE DTC
Ignition on, engine not running.

With a scan tool, read DTCs.

Is the DTC active at this time?

Yes
1. Go To step 2).
No
1. Refer to INTERMITTENT CONDITION .
2. Perform POWERTRAIN VERIFICATION TEST .
2) STOP LAMP SWITCH
Turn the ignition off.

Disconnect the Stop Lamp Switch harness connector.

Measure the resistance between the (Z904) Ground circuit terminal and the (B15) Brake Switch No.1 Signal circuit terminal in the Stop Lamp Switch.

Apply and release the Stop Lamp Switch while monitoring the ohmmeter.

Does the resistance change from below 5.0 ohms to an open circuit?

Yes
1. Go To step 3).
No
1. Replace the Stop Lamp Switch.
2. Perform POWERTRAIN VERIFICATION TEST .
3) (B15) BRAKE SWITCH NO.1 SIGNAL CIRCUIT OPEN

Fig 1: Checking Brake Switch No. 1 Signal Circuit
Courtesy of DAIMLERCHRYSLER CORP.

Turn the ignition off.

Disconnect the C3 PCM harness connector.

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.

Measure the resistance of the (B15 Brake Switch No.1 Signal circuit from the Stop Lamp Switch harness connector to the appropriate terminal of special tool #8815.

Is the resistance below 5.0 ohms?

Yes
1. Go To step 4).
No
1. Repair the open in the (B15) Brake Switch No.1 Signal circuit.
2. Perform POWERTRAIN VERIFICATION TEST .
4) (B16) BRAKE SWITCH NO.2 CIRCUIT SHORTED TO GROUND

Fig 2: Checking Brake Switch No. 2 Signal Circuit
Courtesy of DAIMLERCHRYSLER CORP.

Measure the resistance between ground and the (B16) Brake Switch No.2 Signal circuit in the Stop Lamp Switch harness connector.

Is the resistance below 100 ohms?

Yes
1. Repair the short to ground in the (B16) Brake Switch No.2 Signal circuit.
2. Perform POWERTRAIN VERIFICATION TEST .
No
1. Go To step 5).
5) (Z904) GROUND CIRCUIT OPEN

Fig 3: Checking Ground Circuit
Courtesy of DAIMLERCHRYSLER CORP.

Measure the resistance between the (Z904) Ground circuit and ground in the Stop Lamp Switch harness connector.

Is the resistance below 5.0 ohms?

Yes
1. Go To step 6).
No
1. Repair the open in the (Z904) Ground circuit.
2. Perform POWERTRAIN VERIFICATION TEST .
6) PCM
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.

Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.

Were there any problems found?

Yes
1. Repair as necessary.
2. Perform POWERTRAIN VERIFICATION TEST .
No
1. Replace and program the Powertrain Control Module per Service Information.
2. Perform POWERTRAIN VERIFICATION TEST .