Code 48

CIRCUIT DESCRIPTION
Voltage is supplied to TCM by either the battery (engine off) or the alternator/generator (engine on.)

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. This test determines if the battery is OK.
2. This test determines if a charging problem exists.
3. This test checks for continuity of voltage supply wire to terminals 28 and 37 of the TCM connector.

DIAGNOSTIC AIDS
The ECM automatically increases idle speed when the battery voltage falls below 11.8 volts. If battery voltage is greater than 16V, check the alternator and/or regulator. If the circuit to TCM terminal 28 is open, it has the same effect as pulling the fuse to clear codes. When the ignition is switched off, all codes will be lost. If the circuit to TCM terminal 37 is open, the TCM cannot function. The transmission will start and stay in 4th gear. The "CHECK TRANS" light will not come on at anytime. If system voltage fluctuates outside of the normal 9.1 to 16 volt range, the transmission will be put into backup or safety mode. If normal voltage is reestablished within 3 seconds, normal transmission operation will resume.

CIRCUIT DIAGRAM

Supply Voltage Circuit:

CODE 48 or 49 DIAGNOSTIC CHART

Code 48 Or 49 Diagnostic Chart: