1, 2 and 3 Digit Codes: 20

Name of Code:
20-Switched Battery

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 if the Transmission Control Module (TCM) senses voltage on any of the pressure switch inputs prior to the TCM energizing the relay.

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".

Immediately after a controller reset (ignition key turned to the "run" position or after cranking engine), the TCM verifies that the relay contacts are open by checking for no voltage at the switched battery terminals. After this is verified, the voltage at the solenoid pack pressure switches is checked. There should be no voltage on the pressure switches at this time. The TCM will then activate the relay.

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:
- Short to battery on one or more pressure switch sense circuits
- TCM connector problem
- Defective TCM