1, 2 and 3 Digit Codes: 29

Name of Code:
29 - Throttle Position Signal

When Monitored:
Whenever the engine is running.

Set Condition:
This code is set if the throttle angle goes out of range or if throttle angle changes abruptly (i.e.: faster than the throttle body motion could occur)

Theory of Operation:
The Transmission Control Module (TCM receives the throttle position signal from the Throttle Position Sensor (TPS). The TPS has a 5-volt pull up supplied from the Powertrain Control Module (PCM). The signal is checked for out-of-range as well as intermittency (excessive signal changes).

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:
- Extremely erratic transmission shifting with an intermittent TPS signal just prior to setting the code. If the intermittency does not last long enough to set the code, the customer will say that the transmission violently hunts between gears.

- 89-96 MY - If the fault is set within a given key start, it results in a fixed throttle angle of 24 degrees being used. This results in early harsh downshifts, delayed upshifts and inhibits EMCC.

- 97 MY If this code is set, the TCM will use a "calculated throttle angle" supplied by the PCM over the COD bus. If the COD bus is unavailable, the TCM will use a default throttle angle of 24 degrees for the key start in which the code was set. The TCM will try to use the TPS signal again on the next key start.

Possible Causes:
- Open or shorted TPS signal and/or ground circuits

- TCM connector problems
- Failed TPS or TPS connector (Check PCM DTC's)
- Defective PCM
- Defective TCM