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Test Description

WARNING: This page is about a different car, the 2004 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers in the diagnostic table.

  1. 1:  The OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
  2. 3:  This step will determine if the fault is in the stop lamp switch.
  3. 4:  This step will determine whether there is a short to voltage in the stop lamp circuit between the PCM and the stoplamp switch.
  4. 6:  This step will determine whether there is a short to voltage within the PCM, or a short to voltage in the circuit between the PCM and the stop lamp switch.
DTC P1520

Step Action Yes No
Schematic Reference: Automatic Transmission Controls Schematics 
1  Did you perform a Diagnostic System Check-Engine Controls? Go to Step 2  Go to Diagnostic System Check - Engine Controls in Engine Controls
2
  1. Turn OFF the ignition.
  2. The brake pedal released.
  3. Observe the stop lamps.
Do the stop lamps remain ON?		 Go to Step 3  Go to Step 5 
3 
  1. Disconnect the electrical connector from the stop lamp switch.
  2. Observe the stop lamps.
Do the stop lamps remain ON?		 Go to Step 4  Go to Step 7 
4 
  1. Disconnect the PCM electrical connector.
  2. Ensure the stop lamp switch electrical connector is still disconnected.
  3. Measure the voltage at terminal 1 of the stop lamp switch connector.
Is the voltage more than the specified voltage?		 Go to Step 8  Go to Step 10 
5
  1. Observe the TCC brake switch parameter, using a scan tool.
  2. The brake pedal released.
Does the scan tool indicate that the stop lamp switch is in the released position?		 Go to Symptoms - Engine Controls in Engine Controls Go to Step 6 
6 
  1. Disconnect the PCM electrical connector.
  2. Back out the brake signal circuit terminal.
  3. Reconnect the PCM electrical connector.
  4. Observe the TCC brake switch parameter, using a scan tool.
Does the scan tool indicate the stop lamp switch is in the released position?		 Go to Step 8  Go to Step 10 
7
  1. Check for a misadjusted stop lamp switch.
  2. Adjust the stop lamp switch as necessary.
Was adjustment of the stop lamp necessary?		 Go to Step 11  Go to Step 9 
8 Repair the short to voltage in the brake signal circuit between the stoplamp switch electrical connector and the PCM. Refer to Wiring Repairs in Wiring System.
Is the action complete?		 Go to Step 11  -
9 Replace the stop lamp switch.
Is the action complete?		 Go to Step 11  -
10 Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement in Engine Controls.
Is the action complete?		 Go to Step 11  -
11
  1. Perform the scan tool Clear DTC Information function and road test the vehicle within the Freeze Frame conditions that set the DTC.
  2. Check for DTCs.
  3. Review the scan tool data and if no DTCs are stored the repair is complete.
Are any DTCs displayed on the scan tool?		 Go to Diagnostic Trouble Code (DTC) List/Type  System OK
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