For 1990-2009 cars

### 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
--- | --- | --- | --- | ---
Coolant Level Switch Signal | Lamp OFF | Lamp ON | Lamp OFF | --
Low Reference | -- | Lamp ON | -- | --

### Circuit/System Description

The low engine coolant level indicator lamp on the instrument panel cluster (IPC) is controlled by the body control module (BCM) through the low speed GM LAN Serial Data line to the engine control module (ECM). When the engine coolant level switch is open for 30 seconds or longer indicating low coolant, the BCM will signal the ECM to turn ON the Coolant level lamp. The lamp will also illuminate for approximately 3 seconds during the display test at the start of each ignition cycle.

### Reference Information

#### Schematic Reference

Engine Cooling Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Cooling 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, observe the scan tool coolant level switch. The reading should be OK with the coolant at the proper level.
2. Turn ON the ignition with the engine OFF.
3. Command the instrument cluster indicators ON and OFF with a scan tool.
4. The low coolant indicator lamp should turn ON and OFF on command.
5. The low coolant indicator should be OFF with the engine coolant at the proper level.

### Circuit/System Testing

Important: Circuit/System Verification must be performed before performing the Circuit/System Testing.

1. Ignition OFF, disconnect the harness connector at the coolant level switch.
2. Test for less than 5 ohms of resistance between the ground circuit terminal B and ground.

⇒ | If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the scan tool coolant level switch parameter reads LOW.

⇒ | If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the control module.

4. Install a 3A fused jumper wire between the signal circuit terminal A and the ground circuit terminal B. Verify the scan tool coolant level switch parameter reads OK.

⇒ | If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the control module.

5. If all circuits test normal, test or replace the coolant level switch.

### Component Testing

1. Ignition OFF, disconnect the harness connector at the coolant level switch.
2. Test for infinite resistance between the signal terminal A and the ground circuit terminal B with the switch in the open position.

⇒ | If not the specified value, replace the coolant level switch.

3. Test for less than 5 ohms between the signal terminal A and the ground circuit terminal B with the switch in the closed position.

⇒ | If greater than the specified range, replace the coolant level switch.

### Repair Instructions

• | Instrument Cluster Replacement

• | Radiator Surge Tank Replacement

• | Control Module References for ECM replacement, setup, and programming

### Repair Verification

Verify that the low coolant indicator is OFF with the engine coolant at the proper level.