1, 2 and 3 Digit Codes: 15

Name of Code:
15-Trans Control Relay Circuit

When Monitored:
Ignition key is turned from "off" position to "run" position and/or ignition key is turned from "crank" position to "run" position.

Set Condition:
This code is set when less than 3 volts are present at the relay output (switched battery) terminals at the Transmission Control Module (TCM) when the TCM is energizing the relay.

On 96 MY and 97 model year vehicles, relay output is always sensed, therefore anytime the switched battery drops below 3 volts, the transmission will go into limp-in mode and set the code.

Theory of Operation:
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 16 and 17. It is referred to as "switched battery".

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.

Monitor Condition Verification:
The following conditions must be met for a successful OBDII trip:
- The engine must run for more than two minutes
- The turbine speed must be greater than 600 RPM or the output speed must be greater than 400 RPM.
- 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.

Transmission Effects:
All MY's and calibrations - Relay open limp-in mode.

Possible Causes:
- Relay failure (intermittent relay function caused by oxidized or contaminated relay contacts)
- Short to ground or open circuit in the transmission control relay circuit(s)
- TCM connector problem
- Defective TCM