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
NOTE: Make sure the Stop Lamp Switch is adjusted properly before continuing.

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 OPERATION
Turn the ignition off.

Disconnect the Stop Lamp Switch harness connectors.

Measure the resistance between the (Z904) Ground circuit terminal and the (B15) Brake Switch No.1 Signal 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 when pressing and releasing the brake switch?

Yes
1. Go To step 3).
No
1. Replace the Stop Lamp Switch.
2. Perform POWERTRAIN VERIFICATION TEST .
3) STOP LAMP SWITCH OPERATION
Measure the resistance between the (F942) Fused Ignition Switch circuit terminal and the (B16) Brake Switch No.2 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 when pressing and releasing the Stop Lamp switch?

Yes
1. Go To step 4).
No
1. Replace the Stop Lamp Switch.
2. Perform POWERTRAIN VERIFICATION TEST .
4) (B16) BRAKE SWITCH NO.2 SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE

Fig 1: Checking Brake Switch No. 2 Signal Circuit
Courtesy of DAIMLERCHRYSLER CORP.

Disconnect the C3 PCM harness connector.

Ignition on, engine not running.

Measure the voltage on the (B16) Brake Switch No.2 Signal circuit in the Stop Lamp Switch harness connector.

Is the voltage above 1.0 volt?

Yes
1. Repair the short to battery voltage in the (B16) Brake Switch No.2 Signal circuit.
2. Perform POWERTRAIN VERIFICATION TEST .
No
1. Go To step 5).
5) (B15) BRAKE SWITCH NO.1 SIGNAL CIRCUIT SHORTED TO GROUND

Fig 2: Checking Brake Switch No. 1 Signal Circuit
Courtesy of DAIMLERCHRYSLER CORP.

Turn the ignition off.

Measure the resistance between ground and the (B15) Brake Switch No.1 Signal circuit in the Stop Lamp Switch harness connector.

Is the resistance below 100 ohms?

Yes
1. Repair the short to ground in the (B15) Brake Switch No.1 Signal circuit.
2. Perform POWERTRAIN VERIFICATION TEST .
No
1. Go To step 6).
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 .