P0551-POWER STEERING PRESSURE SWITCH PERFORMANCE

For a complete wiring diagram Refer to Section 8W.

Theory of Operation

The power steering switch is used to enable quick spark and fuel corrections for high power steering loads to maintain target idle speed. The power steering switch rationality monitors the switch input during high vehicle speed conditions when the steering wheel cannot be turned far enough to reach the high-pressure switch point. If the power steering switch input remains at a high-pressure condition at high vehicle speeds, a failure timer will increment.

When Monitored:
With the ignition key on and engine running.
Set Condition:
With the vehicle above 40 mph for over 30 seconds, the power steering pressure switch remains open. Two Trip Fault. Three good trips to turn off the MIL.

Possible Causes

(K66) P/S SWITCH SIGNAL CIRCUIT OPEN

(K66) P/S SWITCH SIGNAL CIRCUIT SHORTED TO GROUND

(Z988) GROUND CIRCUIT OPEN

POWER STEERING PRESSURE SWITCH

PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).

Diagnostic Test

1.ACTIVE DTC

NOTE: It may be necessary to drive the vehicle to meet the conditions to set this DTC, try to repeat the conditions in which the fault originally set by reviewing the Freeze Frame data.

Is the DTC Active or Pending at this time?

Yes

Go To 2

Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

2.POWER STEERING PRESSURE SWITCH

Did the Power Steering Pressure Switch status change from High to Low when connecting and disconnecting the jumper wire?

Yes

Replace the Power Steering Pressure Switch.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Go To 3
NOTE: Remove the jumper wire before continuing.

3.(K66) P/S SWITCH SIGNAL CIRCUIT OPEN

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.

Is the resistance below 5.0 ohms?

Yes

Go To 4

Repair the open in the (K66) P/S Switch Signal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

4.(K66) P/S SWITCH SIGNAL CIRCUIT SHORTED TO GROUND

Is the resistance below 100 ohms?

Yes

Repair the short to ground in the (K66) P/S Switch Signal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Go To 5

5.(Z988) GROUND CIRCUIT OPEN

Is the resistance below 100 ohms?

Yes

Go To 6

Repair the open in the (Z988) Ground circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

6.PCM

NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.

Were there any problems found?

Yes

Repair as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Replace and program the Powertrain Control Module per Service Information.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)