Circuit Description
This diagnostic test functions on the assumption that sudden decrease in a non-drive wheel speed must be caused by a brake application. Non-drive wheel speed and stop lamp switch status are supplied to the powertrain control module (PCM) through serial data from the electronic brake control module (EBCM). If there is a 2.5 mph or greater decrease of non-drive wheel speed in 0.4 seconds and a transition of the torque converter clutch (TCC) or extended travel contacts of the TCC brake switch without a transition of the stop lamp brake switch, DTC P1574 is set.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1574 Stop Lamp Switch Circuit
Conditions for Running the DTC
| • | DTCs P0502, P0503, P0719, P0724, P1575 and P1602 not set. |
| • | Traction control and antilock brake systems have not failed. |
| • | Traction control and antilock brake systems are not active. |
| • | Non-drive wheel speed goes above 32.2 km/h (20 mph) and then does not go below 6.4 km/h (4 mph). |
Conditions for Setting the DTC
A 2.5 mph or greater decrease in non-drive wheel speed in 0.4 second and extended travel brake switch or TCC brake switch indicating brakes applied and no transition noticed in the stop lamp contacts of the stop lamp switch.
Action Taken When the DTC Sets
The PCM will set the stop lamp switch status to not applied.
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | No message will be displayed. |
Conditions for Clearing the DTC
| • | A History DTC will clear after 40 consecutive warm-up cycles with no failures of any non-emission related diagnostic test. |
| • | A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail. |
| • | Use a scan tool to clear DTCs. |
| • | Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. |
Diagnostic Aids
DTC P1574 indicates the stop lamp switch signal to the EBCM or the EBCMs ability to send the stop lamp switch signal to the PCM has failed. Refer to ABS/TCS DTCs for diagnosis of the stoplamp switch signal and the EBCM.
Step | Action | Yes | No |
|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 |
Are any DTCs that begin with a "C" also set? | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | Go to Step 3 |
3 | Repair the short to voltage on the stop lamp switch signal circuit. Did you find and correct the condition? | Go to Step 4 | -- |
4 |
Does the DTC set? | Go to Step 2 | System OK |
