GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC K Sierra - 4WD 🢒 Body and Accessories 🢒 Instrument Panel, Gauges, and Console 🢒 Engine Coolant Level Switch/Sensor Diagnosis

Object Number: 366336 Size: SF
Engine Controls Component Views
Cell 21: G102, G104, Cruise Control Module
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Engine Coolant Level switch is located in the radiator surge tank. The Engine Coolant Level Switch is a Float Type Switch. The PCM supplies a voltage to the Engine Coolant Level switch. The Engine Coolant Level switch is a normally open switch. When the coolant level is within an acceptable range the Engine Coolant Level switch closes. The switch opens when the engine coolant level drops below a predetermined amount. When the PCM detects a high signal voltage (switch open) from the Engine Coolant Level switch the PCM sends a class 2 message to the Instrument Panel Cluster (IPC). The IPC displays the LOW COOLANT message.

Diagnostic Aids

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

    • The following may cause an intermittent:
       - Poor connections: Check for adequate terminal tension. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
       - Corrosion
       - Mis-routed harness
       - Rubbed through wire insulation
       - Broken wire inside the insulation
       - A float that is stuck
    • For an intermittent, refer to Symptoms .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This steps tests the Engine Coolant level sensor signal circuit between the PCM and the sensor.

    2.

  2. This steps tests the Engine Coolant level sensor ground circuit between the PCM and the sensor.

    3.

  3. This steps tests the Engine Coolant level sensor signal circuit for a short to ground.

    4.

  4. This steps tests for an open in the Engine Coolant level sensor signal circuit between the PCM and the Engine Coolant level sensor .

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

Important: This table assumes the coolant level is at the proper level or the coolant level is low and the Low Coolant Level Lamp never illuminated. If the coolant level is low, refer to Loss of Coolant in Engine Cooling.

  1. Turn ON the ignition leaving the engine OFF.
  2. Install a scan tool.
  3. Select the Diagnostic Circuit Check and then the Class 2 Message Monitor.

Does the scan tool display the Instrument Panel Cluster (IPC) as active?

--

Go to Step 3

Go to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gauges and Console

3

Is the customers concern that the Low Coolant Level Lamp is on at all times?

--

Go to Step 4

Go to Step 7

4

  1. Disconnect the Engine Coolant Level switch.
  2. Measure the voltage of the Engine Coolant Level switch signal circuit using the DMM J 39200 connected to ground. Refer to Measuring Voltage in Wiring Systems.

Does the DMM display near the specified value?

B+

Go to Step 5

Go to Step 10

5
  1. Jumper the Engine Coolant Level switch signal circuit to battery ground using a fused jumper wire. Refer to Using Fused Jumper Wires in Wiring Systems.
  2. Monitor the Low Coolant Level parameter using the scan tool.

Does the scan tool display Low Coolant Level as NO?

--

Go to Step 6

Go to Step 17

6

Jumper the Engine Coolant Level switch signal circuit to the Engine Coolant Level switch ground circuit using a fused jumper wire. Refer to Using Fused Jumper Wires in Wiring Systems.

Does the scan tool display Low Coolant Level as NO?

--

Go to Step 11

Go to Step 15

7
  1. Disconnect the Engine Coolant Level switch.
  2. Measure the voltage of the Engine Coolant Level switch signal circuit using the DMM J 39200 connected to ground. Refer to Measuring Voltage in Wiring Systems.

Does the DMM display near the specified value?

B+

Go to Step 8

Go to Step 9

8
  1. Jumper the Engine Coolant Level switch signal circuit to battery ground using a fused jumper wire. Refer to Using Fused Jumper Wires in Wiring Systems.
  2. Monitor the Low Coolant Level parameter using the scan tool.

Does the scan tool display Low Coolant Level as YES?

--

Go to Step 17

Go to Step 12

9

Important: Disconnecting the PCM connector may eliminate the short to ground if the signal circuit is shorted to another PCM circuit.

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C1 located on the same side as the manufacturer's logo. Refer to Powertrain Control Module Replacement/Programming .
  3. Test continuity of the Engine Coolant Level switch signal circuit using the DMM J 39200 connected to ground. Refer to Testing for Continuity in Wiring Systems.

Does the DMM display continuity?

--

Go to Step 13

Go to Step 17

10

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C1 located on the same side as the manufacturer's logo. Refer to Powertrain Control Module Replacement/Programming .
  3. Test continuity of the Engine Coolant Level switch signal circuit using the DMM J 39200 . Refer to Testing for Continuity in Wiring Systems.

Does the DMM display continuity?

--

Go to Step 16

Go to Step 14

11
  1. Inspect for poor connections at the Engine Coolant Level switch harness connector. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
  2. If you find a poor connection, repair the terminal as necessary.

Did you find and repair the condition?

--

System OK

Go to Step 12

12

Replace the Engine Coolant Level switch. Refer to Radiator Surge Tank Replacement in Engine Cooling.

Is the action complete?

--

System OK

--

13

Repair the Engine Coolant Level switch signal circuit for a ground. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

System OK

--

14

Repair the Engine Coolant Level switch signal circuit for an open. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

System OK

--

15

Repair the Engine Coolant Level switch ground circuit for an open. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

System OK

--

16
  1. Inspect for poor PCM connections at the PCM harness connector. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
  2. If you find a poor connection, repair the terminal as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and repair the condition?

--

System OK

Go to Step 17

17

Important:: Program the replacement PCM. Refer to Powertrain Control Module Replacement/Programming .

Replace the PCM.

Is the replacement complete?

--

System OK

--