GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2009 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Brakes 🢒 Air Brakes 🢒 Low Air Indicator Malfunction

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Low Air Pressure Signal

1

1

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--

Ground

--

1

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1. Low Air Indicator Malfunction

Circuit/System Description

The air pressure switch opens when the air pressure is between 64-76 psi, and closes when it detects the air pressure is below 60 psi.

Reference Information

Schematic Reference

Air Brake System Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Air Brake System Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
  1. Ignition ON, with a scan tool command the IPC lamp test ON and OFF. The Low Air indicator should turn ON and OFF.
    2. ⇒If the Low Air indicator does not turn ON and OFF, replace the IPC.
  2. Engine Running, verify the air pressure gauge reads between 64-76 psi.
    3. ⇒If not the specified value, refer to Air Brake System Testing.

Circuit/System Testing
  1. Ignition OFF, disconnect the harness connector at the primary low air pressure switch.
  2. Test for less than 1 ohm between the ground circuit terminal A and ground.
    3. ⇒If not the specified value, test the ground circuit for an open/high resistance.
  3. Verify the low air pressure warning indicator is OFF.
    4. ⇒If not the specified value, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the IPC.
  4. Install a 3A fused jumper wire between the signal circuit terminal B and ground. Verify the low air pressure indicator is ON.
    5. ⇒If not the specified value, test the signal circuit for an open/high resistance. If the circuit tests normal, test or replace the primary low air pressure switch.
  5. Ignition OFF, disconnect the harness connector at the secondary low air pressure switch.
  6. Test for less than 1 ohm between the ground circuit terminal A and ground.
    7. ⇒If not the specified value, test the ground circuit for an open/high resistance.
  7. Verify the low air pressure warning indicator is OFF.
    8. ⇒ If not the specified value, test the signal circuit terminal B for a short to ground. If the circuit tests normal, replace the IPC.
  8. Install a 3A fused jumper wire between the signal circuit terminal B and ground. Verify the low air pressure indicator is ON.
    9. ⇒If not the specified value, test the signal circuit for an open/high resistance. If the circuit tests normal, test or replace the secondary low air pressure switch.
  9. If all circuits test normal, test or replace the low air pressure sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Low Air Pressure Switch Replacement
    •  Control Module References for module replacement, setup, and programming