For 1990-2009 cars
Cell 20: Idle Air Control
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The power steering pressure (PSP) switch is normally open to ground, and the powertrain control module (PCM) terminal will be near battery voltage. Turning the steering wheel increases power steering oil pressure and its load on an idling engine. The PSP switch will close before the load can cause a poor idling condition. Closing the switch causes the PCM voltage signal to read less than one volt. The PCM will increase the throttle opening in order to prevent engine load stall.

### Diagnostic Aids

Check for any of the following items:

• | A PSP switch that will not close, or loss of ground at the PSP switch may cause the engine to stall when power steering loads are high.

• | A PSP switch that will not open or a signal line shorted to ground may affect idle quality.

An intermittent malfunction may be caused by a fault in the PSP sensor circuit. Inspect the wiring harness and components for any of the following conditions:

• | Backed out terminals.

• | Improper mating of terminals.

• | Broken electrical connector locks.

• | Improperly formed or damaged terminals.

• | Faulty terminal to wire connections.

• | Physical damage to the wiring harness.

• | A broken wire inside the insulation.

• | Corrosion of electrical connections, splices, or terminals.

### Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

1. This step checks for the PCM signal voltage and for an open or a short to ground in the signal circuit, or for a malfunctioning PCM.

2. This step checks for a poor ground connection at the power steering pump and for a malfunctioning PSP switch.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you Perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Start the engine.
2. Run the engine until the normal operating temperature is attained.
3. Turn OFF all of the accessories.
4. Observe the PSP switch parameter on the scan tool.
5. With the steering wheel straight, the scan tool should read OFF.
6. Turn the steering wheel all the way to the right or left, the scan tool should read ON.

Does the PSP switch fail either test?

--

Go to Step 3

Go to Rough, Unstable, or Incorrect Idle and Stalling

3 |

1. Turn ON the ignition.
2. Disconnect the PSP switch electrical connector.
3. Using a DMM, measure the voltage from the PSP switch connector to ground (harness side).

Is the voltage near the specified value?

B+

Go to Step 4

Go to Step 5

4 |

1. Connect a test light to B+ and probe the PSP switch connector (switch side).
2. Turn ON the ignition.

Is the test light ON when the steering wheel is turned all the way to the right or left?

--

Go To Diagnostic Aids

Go to Step 6

5 |

1. Check for an open or a short to ground in the PSP signal circuit between the PCM and the PSP switch.
2. Repair as necessary.

Was a repair necessary?

--

Go to Step 9

Go to Step 8

6 |

1. Check for a poor ground connection at the power steering pump.
2. Repair as necessary.

Was a repair necessary?

--

Go to Step 9

Go to Step 7

7 | Replace the PSP switch. Refer to PSP Switch Replacement . Is the action complete? | -- | Go to Step 9 | --
8 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 9 | --
9 | Operate the vehicle within the conditions under which the original symptom was noted. Does the system now operate properly? | -- | System OK | Refer To Diagnostic Aids