GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1998 🢒 DeVille 🢒 Engine 🢒 Engine Controls - 4.0L and 4.6L 🢒 DTC P0550 Power Steering Pressure (PSP) Switch Circuit

Object Number: 244405 Size: SF
Engine Controls Components
Cell 20: IAC Valve and PSP, Oil Level Switches
OBD II Symbol Description Notice
ESD Notice

Circuit Description

The Power Steering Pressure (PSP) switch is a normally closed switch which opens when power steering pressure exceeds 450 to 650 psi. The PSP switch closes again when pressure drops below 100 to 450 psi. This diagnostic test monitors the power steering pressure switch. When a load is placed on the power steering such as full lock, the switch opens. When driving over 45 mph, no load condition, the switch is closed. DTC P0550 sets when the vehicle is above 45 MPH and the power steering pressure switch signal is open.

Conditions for Running the DTC
    •  Engine running.
    •  Vehicle speed 45 MPH or greater.

Conditions for Setting the DTC

Power steering pressure switch open for 60 seconds.

Action Taken When the DTC Sets

PCM limits desired idle speed to a minimum of 800 RPM.

    •  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

Check for intermittent contact at the power steering pressure switch or stretching of the harness causing an intermittent open circuit.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

  1. Checking if switch will respond to pressure.

    2.

  2. If display stays Hi Press., there is an open or short to ground in the circuitry.

    3.

  3. Checking if the ignition feed circuit or fuse is open.

    4.

  4. Checking if the power steering pressure switch is open. With switch bypassed, input should be Normal.

    5.

  5. Checking if the power steering pressure switch input circuit is open or shorted to ground.

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. Connect a scan tool.
  2. View the PSP Switch display.
  3. With the engine running turn the steering wheel from straight ahead to full left lock and back to straight ahead.

Did display change from Normal to Hi Press. and back to Normal?

--

Go to Diagnostic Aids

Go to Step 3

3

Turn the eng OFF key ON.

Does the display remain Hi Press.?

--

Go to Step 4

Go to Step 8

4

  1. Disconnect the power steering pressure switch connector.
  2. Using DMM J 39200 measure voltage to ground at power steering pressure switch connector terminal B (harness side).

Is the voltage the same or more than the value specified?

10 volts

Go to Step 5

Go to Step 10

5

Jumper power steering pressure switch connector terminals A and B together (harness side).

Does the display read Hi Press.?

--

Go to Step 6

Go to Step 11

6

  1. Record the fluid life indexes, turn the key to OFF and wait 30 seconds.
  2. Disconnect PCM connector C1.
  3. Leave jumper in place.
  4. Turn the key ON, measure voltage to ground at PCM connector C1 terminal 35 (harness side).

Is the voltage the same or more than the value specified?

10 volts

Go to Step 7

Go to Step 12

7
  1. Check terminal contact at PCM connector C1 terminal 35.
  2. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis

Go to Step 17

8
  1. Key ON, engine OFF.
  2. Disconnect power steering pressure switch.

Does the display read Normal?

--

Go to Step 9

Go to Step 11

9
  1. Record the fluid life indexes, turn the key to OFF and wait 30 seconds.
  2. Disconnect PCM connector C1.
  3. Turn the key ON.
  4. Measure voltage to ground at PCM connector C1 terminal 35 (harness side).

Is voltage the same or less than the value specified?

0.5 volts

Go to Step 7

Go to Step 13

10

Check the power steering ignition feed circuit fuse.

Is the fuse blown?

--

Go to Step 14

Go to Step 15

11
  1. Check the terminal contact at power steering pressure switch.
  2. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis

Go to Step 16

12

Repair open or short to ground in the power steering pressure switch input circuit.

Is the repair complete?

--

Go to Powertrain Control Module Diagnosis

--

13

Repair short to voltage on the power steering pressure switch input circuit.

Is the repair complete?

--

Go to Powertrain Control Module Diagnosis

--

14

Replace fuse and check / repair short to ground in the power steering ignition feed circuit or the PSP input circuit.

Is the repair complete?

--

Go to Powertrain Control Module Diagnosis

--

15

Repair open in the power steering ignition feed circuit.

Is the repair complete?

--

Go to Powertrain Control Module Diagnosis

--

16

Replace power steering pressure switch.

Is the replacement complete?

--

Go to Powertrain Control Module Diagnosis

--

17

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Is the replacement complete?

--

Go to Powertrain Control Module Diagnosis

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