With 4L80-E Automatic Transmission

4L80-E AUTOMATIC TRANSMISSION

DTC 37/38 Chart:

Brake Switch Circuit:

CIRCUIT DESCRIPTION
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.

DIAGNOSTIC TROUBLE CODE (DTC) 37 WILL SET WHEN
- CKT 420 is open.
- Vehicle speed is less than 5 mph for greater than 6 seconds.
- Then vehicle speed is between 5 mph and 20 mph for greater than 6 seconds.
- Then vehicle speed is greater than 20 mph for greater than 6 seconds.
- For a total of seven times.

DIAGNOSTIC TROUBLE CODE (DTC) 38 WILL SET WHEN
- CKT 420 has constant voltage.
- 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 total of seven times.

ACTION TAKEN (PCM WILL DEFAULT TO)
- No TCC.
- No 4th Gear in Hot Mode.

DTC 37/38 WILL CLEAR WHEN
Fault condition no longer exists.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. This test checks for voltage at the 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).