P1520
DTC P1520
Circuit Description
The powertrain control module (PCM) will detect a malfunction when the stop lamp switch is in the closed position, and the stop lamps are ON, the stop lamp switch should be open. The DTC P1520 is only supported on vehicles with an automatic transmission. If the stop lamp switch is closed, the PCM will not allow the torque converter clutch (TCC) lock-up to occur. The PCM also uses the stop lamp switch input for fuel cut-off control.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1520 Stop Lamp Switch Circuit
Conditions for Running the DTC
^ The engine is running.
^ The vehicle speed is more than 30 km/h (19 mph).
Condition for Setting the DTC
The stop lamp switch always remains in the ON position.
Action Taken When the DTC Sets
^ The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.
^ The PCM stores the conditions which were present when the DTC set as Freeze Frame data.
Conditions for Clearing the MIL/DTC
^ The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
^ The DTC clears after 40 consecutive warm-up cycles have occurred without a fault.
^ A DTC can be cleared by using the scan tool Clear DTC Information function.
Diagnostic Aids
An intermittent malfunction may be caused by a fault in the stop lamp switch electrical circuit. Inspect the wiring harness and the components for any of the following conditions:
^ Any backed-out terminals
^ Any improper mating of terminals
^ Any broken electrical connector locks
^ Any improperly formed or damaged terminals
^ Any faulty terminal-to-wire connections
^ Any physical damage to the wiring harness
^ A broken wire inside the insulation
^ Any corrosion of the electrical connections, the splices, or the terminals
Repair any electrical circuit faults that were found.
The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
1. The Diagnostic System Check - Vehicle, 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.
3. This step will determine if the fault is in the stop lamp switch.
4. This step will determine whether there is a short to voltage in the stop lamp circuit between the PCM and the stop lamp switch.
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.
