Powertrain Controls - ECM/PCM

Diagnostic Trouble Code 38 Chart:

Brake Switch Circuit:

CIRCUIT DESCRIPTION
The transmission Torque Converter Clutch (TCC) brake switch is used to indicate brake pedal status. The normally closed brake switch supplies a B+ signal on CKT 420 to the Powertrain Control Module (PCM). The signal voltage is opened when the brakes are applied. The PCM uses this signal to de-energize the TCC solenoid when the brakes are applied.

DIAGNOSTIC TROUBLE CODE (DTC) 38 WILL SET WHEN
CKT 420 has constant voltage.
- Vehicle speed is less than 5 mph.
- Then vehicle speed is greater than 20 mph for greater than 6 seconds.
- Then vehicle speed is between 5 mph and 20 mph for greater than 6 seconds.
- For a complete total of seven times.

ACTION TAKEN (PCM DEFAULT)
An incorrect brake signal can affect TCC scheduling. Also, an incorrect brake signal can inhibit fourth gear operation, if in hot mode. DTC 38 will be stored in PCM memory, but, will not turn "ON" the Malfunction Indicator Lamp (MIL).

DTC 38 Will Clear When
Fault condition no longer exists.

DTC CHART TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. This test checks for voltage at brake switch.
2. This test checks the brake switch.
3. This test checks CKT 420 at the PCM.

DIAGNOSTIC AIDS
Check customer driving habits and/or unusual traffic conditions (i.e. stop and go expressway traffic).