Powertrain Controls - ECM/PCM

DTC 37:

TCC Brake Switch Wiring Schematic:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) monitors brake switch activity through PCM terminal "A18." The brake switch is a normally closed switch that opens to interrupt system voltage to the PCM input when the brake pedal is applied.

DIAGNOSTIC TROUBLE CODE (DTC) 37 WILL SET WHEN
Vehicle speed is maintained above 35 mph for 10 seconds and back to 0 mph for 4 consecutive times without the PCM sensing a voltage change on circuit 420 (displayed "RELEASED" to "APPLIED" on Scan tool).

ACTION TAKEN (PCM) WILL DEFAULT TO
The PCM will not illuminate the Malfunction Indicator Lamp (MIL). If the switch has failed in an open state, the Torque Converter Clutch (TCC) will not engage.

DTC 37 WILL CLEAR WHEN
A current DTC 37 will clear when the PCM begins detecting "APPLIED" to "RELEASED" transitions. A History DTC 37 will clear after 50 consecutive ignition key cycles without a current DTC 37 being stored.

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

1. This test checks for voltage at brake switch.
2. This test simulates brake switch closed or brakes "OFF."
3. This test checks circuit 420 from brake switch to PCM.
4. This test opens circuit 420 and simulates brakes being applied.

DIAGNOSTIC AIDS
A DTC 37 can be caused by a misadjusted brake switch or a poor connection. Also check customer driving habits and / or unusual traffic conditions (i.e. stop and go expressway traffic).