DTC P1579 P/N to D/R at High Throttle Angle - Power Reduction Mode Active. Cadillac Concours 1996

For 1990-2009 cars
Engine Controls Components
IAC Valve and PSP/ Oil Level/ TR Switches
OBD II Symbol Description Notice
ESD Notice

### Circuit Description

This diagnostic test is used to detect the vehicle transaxle being placed in gear under conditions that may cause damage to the vehicle powertrain or create an unsafe condition. When such a condition exists, DTC P1579 is set and engine power will be reduced by disabling fuel to individual cylinders.

### Conditions for Setting the DTC

#### Test Conditions

DTCs P0122 and P0123 not set.

#### Failure Conditions

• | Gear selection from Park or Neutral to Drive or Reverse.

• | Vehicle speed less than 6 MPH.

• | Engine speed greater than 2000 RPM.

• | Throttle angle of 20 degrees or greater.

### Action Taken When the DTC Sets

• | PCM will retard spark and disable fuel to individual cylinders to reduce engine power.

• | The Malfunction Indicator Lamp (MIL) will not illuminate.

• | The PCM will command a message to be displayed.

• | The PCM may record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records.

### Conditions for Clearing the Message/DTC

• | The PCM will turn the message OFF after one run and pass of the diagnostic test.

• | A History DTC will clear after forty consecutive warm-up cycles with no failures of any non-emission related diagnostic test.

• | A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.

• | Use a scan tool to clear DTCs.

• | Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in PCM Description and Operation.

### Diagnostic Aids

If the drivers actions caused this DTC to set, clear the DTC and inform customer of proper shift procedure.

Manipulate the wire harness while watching the scan tool display looking for opens and shorts.

Reviewing the Failure Rec. may help diagnose an intermittent failure by showing how long ago and under what conditions the DTC set.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to A Powertrain On Board Diagnostic (OBD) System Check
2 | Since this DTC will set when the vehicle is shifted into DRIVE / REVERSE under possibly damaging conditions, check with the customer to verify the conditions under which the DTC set. Did the drivers actions cause this DTC to set? | -- | Fault not present. Refer to Diagnostic Aids | Go to Step 3

3

1. Check for proper adjustment of the transaxle range switch and for poor terminal contact at the switch and the PCM.
2. Repair either condition if needed.

Was a repair performed?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Fault not present. Refer to Diagnostic Aids