Transmission Control System
CODE NUMBERScan tool: 15
General scan tool: P1768
CODE NAME
Relay always off (Relay contacts are stuck open)
CODE DESCRIPTION
Technical Description
The Transmission Control Relay is used to supply power to the solenoid pack when the transmission is in normal operating mode. When the relay is off, no power is supplied to the solenoid pack and the transmission is in "limp-in" mode. The relay output is fed back to the TCM through pins 56 and 57.
After a controller reset (ignition key turned to the "run" position or after cranking engine), the controller energizes the relay. Prior to this the TCM verifies that the contacts are open by checking for no voltage at the switched battery terminals. After the relay is energized, the TCM monitors the terminals to verify that the voltage is greater than 3 volts.
Check Area
Ignition key is turned from "off" position to "run" position and/or ignition key is turned from "crank" position to "run" position. The following conditions must be met for a successful OBD II trip:
- The engine must run for more than two minutes.
- The turbine speed must run for more than two minutes.
- If the transmission is below normal operating temperature, all forward gears must be applied for 3.5 seconds each and the transmission must be in either "park" or "neutral" for 3.5 seconds.
- If the transmission is hot, all forward gears must be applied for 1.5 seconds each and the transmission must be in either "park" or "neutral" for 1.5 seconds.
- No MIL lamp trouble codes have occurred or recurred.
Set Conditions
This code is set when less than 3 volts are present at the transmission Control Relay output terminals at the Transmission Control Module (TCM) when the TCM is energizing the relay.
Transmission Effects
Relay outputs is always sensed, therefore anytime the switched battery drops below 3 volts, the transmission goes into limp-in mode and set the code.
PROBABLE CAUSE
- Malfunction of relay (open contacts)
- Harness or connector between relay coil and TCM open or short-circuited
- Harness or connector between relay output and TCM open-circuited
- Relay supply lines open-circuited
- Relay ground open-circuited
- Malfunction of TCM
DIAGNOSTIC CHART