Engine Cooling System: Diagnosis Chevrolet Silverado Classic 2500 HD

DIAGNOSTIC CODE INDEX

DIAGNOSTIC CODE INDEX

Diagnostic Starting Point - Engine Cooling

Begin the system diagnosis with the Diagnostic System Check - Vehicle . The Diagnostic System Check will provide the following information

1. The identification of the control modules which command the system.
2. The ability of the control modules to communicate through the serial data circuit.
3. The identification of any stored diagnostic trouble codes DTCs and their status.

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

Scan Tool Output Controls

PCM - 4.2L, 5.3L

Scan Tool Data List

PCM - 2.4L

Circuit Description

The powertrain control module (PCM) controls the low speed cooling fan operation by grounding the low speed fan relay control circuit with an internal solid state device called a driver. For high speed cooling fan operation, the PCM grounds the high speed and S/P relay control circuit at the same time the low speed control circuit is grounded. Battery positive voltage is supplied to the low speed, high speed, and S/P fan relays. When the PCM is commanding a fan relay ON, the voltage of the control circuit should be low, near 0 volts. When the PCM is commanding a fan relay OFF, the voltage potential of the control circuit should be high, near battery voltage.

The PCM monitors the relay control circuits for the following conditions

1. Short to ground
2. Short to voltage
3. An open circuit

If the PCM detects an improper voltage level on the low or high speed driver circuits, then code P0480 or P0481 will set and the effected driver will be disabled.

1. Cooling fan relay 1 control circuit refers to the low speed cooling fan relay
2. Cooling fan relay 2 control circuit refers to the high speed cooling fan relay

DTC Descriptors

This diagnostic procedure supports the following DTCs

1. DTC P0480 Cooling Fan Relay 1 Control Circuit
2. DTC P0481 Cooling Fan Relay 2 Control Circuit

Conditions for Running the DTC

1. The ignition voltage is between 8-18 volts.
2. The engine speed is more than 40 RPM.
3. The ECM driver transitions from ON to OFF or from OFF to ON.

Conditions for Setting the DTC

1. P0481-The PCM detects an open circuit on the high speed cooling fan relay control circuit.
2. P0480-The PCM detects an open on the low speed cooling fan relay control circuit.
3. The above condition is present for one second.

Action Taken When the DTC Sets

1. The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
2. The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

Conditions for Clearing the MIL/DTC

1. The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.
2. The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. Use the scan tool Clear DTC Information function.

Diagnostic Aids

1. If the condition is not present, refer to «Testing for Intermittent Conditions and Poor Connections»(ref-277884-S20700666652008012100000) .
2. Review the Freeze Frame/Failure Records vehicle mileage since the diagnostic test failed. This may help determine how often the condition that caused the DTC to be set occurs.

The powertrain control module (PCM) uses the ECT sensor to monitor the engine for an over temperature condition. This condition occurs when the coolant temperature is above 132°C (270°F). When an over temperature condition is present, DTC P1258 will set. The PCM will disable two groups of four cylinders by turning OFF the fuel injectors. By switching between the 2 groups of cylinders, the PCM is able to reduce the temperature of the coolant.

DTC Descriptor

This diagnostic procedure supports the following DTC

DTC P1258 Engine Coolant Overtemperature - Protection Mode Active

1. DTCs P0117, P0118, P1114, and P1115 are not active.
2. The engine is running.

The engine coolant temperature is above 132°C (270°F) for 10 seconds or more.

1. The PCM will illuminate the malfunction indicator Lamp (MIL) during the first trip in which the diagnostic test has been run and failed.
2. The PCM will signal the instrument panel cluster (IPC) to turn ON the Service Engine Soon indicator.
3. The PCM will alternately disable two groups of four cylinders by turning OFF the fuel injectors.
4. The PCM will store conditions which were present when the DTC set as Freeze Frame and File Records data.

1. The PCM will turn the MIL OFF after 3 consecutive trips that the diagnostic has been run and passed.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using the scan tool Clear DTC Information function.

DTC P1258

Symptoms - Engine Cooling

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the Cooling System. Refer to «Checking Aftermarket Accessories»(ref-277884-S30236091172008012100000) .
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Inspect the surge tank reservoir for the proper coolant level.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «Engine Overheated Indicator Always On»(ref-277850-S26886649882008012100000)
2. «Engine Coolant Temperature Indicator Always On»(ref-277850-S39579188432008012100000)
3. «Low Engine Coolant Indicator Always On»(ref-277850-S04089153232008012100000)
4. «Engine Overheating»(ref-277850-S30827121042008012100000)
5. «Loss of Coolant»(ref-277850-S02036182982008012100000)
6. «Thermostat Diagnosis»(ref-277850-S06519789172008012100000)
7. «Coolant Heater Inoperative (Gasoline)»(ref-277850-S36264965592008012100000) or «Coolant Heater Inoperative (Diesel)»(ref-277850-S34465461372008012100000)
8. «Engine Fails To Reach Normal Operating Temperature»(ref-277850-S22219594362008012100000)
9. «Fan Clutch Diagnosis»(ref-277850-S36202417052008012100000)

Diagnostic Instructions

1. Perform the «Diagnostic System Check - Vehicle»(ref-277883-S07139257572008012100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-277883-S33769936482008012100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-277883-S17347055992008012100000) provides an overview of each diagnostic category.

Diagnostic Fault Information

Low Engine Coolant Indicator Always On

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the coolant level switch.
2. Install a 3A fused jumper wire between the signal circuit terminal and ground.
3. Engine running, verify the low coolant indicator turns OFF. If the indicator does not turn OFF, test the signal circuit for an open/high resistance. If the indicator turns OFF, test the ground circuit for an open/high resistance.
4. If all circuits test normal, replace the coolant level switch.

Test the engine coolant heater cord for an open or short to ground.

1. If open or shorted, replace the coolant heater cord. If the heater tests normal, replace the coolant heater power cord.

Thermostat Test Procedure Using Tempil Sticks

The coolant thermostat can be tested using a temperature (tempil) stick. The temperature stick is a pencil like device. It has a wax material containing certain chemicals which melt at a given temperature. Temperature sticks can be used to determine a thermostat's operating range, by rubbing 87°C (188°F) and 97°C (206°F) sticks on the thermostat housing.

1. Use a tempil stick in order to find the opening and the closing temperatures of the coolant thermostat. J 24731 -188 tempil stick melts at 87°C (188°F). See «Special Tools»(ref-277850-S19943780362008012100000) . The thermostat should begin to open. J 24731 -206 tempil stick melts at 97°C (206°F). See «Special Tools»(ref-277850-S19943780362008012100000) . The thermostat should be fully open.
2. Replace the coolant thermostat if it does not operate properly between this temperature range.

Thermostat Test Procedure Using Glycol

Inspect the operation of the thermostat by hanging the thermostat on a hook in a 50/50 percent solution of DEX-COOL® and clean drinkable water.

In order to inspect if the thermostat valve is opening properly, perform the following test

1. Completely submerge the thermostat in the glycol solution. The solution should be 11°C (22°F) above the temperature indicated on the thermostat valve.
2. Thoroughly agitate the solution. Under these conditions, the thermostat valve should open.

In order to inspect if the thermostat valve is closing properly, perform the following test

1. Completely submerge the thermostat in a glycol solution. The solution should be 6°C (10°F) below the temperature indicated on the thermostat valve.
2. Thoroughly agitate the solution. Under these conditions, the thermostat valve should close completely.

1. Perform the «Diagnostic System Check - Vehicle»(ref-277883-S07139257572008012100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-277883-S33769936482008012100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-277883-S17347055992008012100000) provides an overview of each diagnostic category.

1. Test the engine coolant heater for an open or short to ground. If open or shorted, replace the heater.
2. If the heater tests normal, replace the coolant heater power cord.

1. Perform the «Diagnostic System Check - Vehicle»(ref-277883-S07139257572008012100000) prior to using this diagnostic procedure.
2. Review «Strategy Based Diagnosis»(ref-277883-S33769936482008012100000) for an overview of the diagnostic approach.
3. «Diagnostic Procedure Instructions»(ref-277883-S17347055992008012100000) provides an overview of each diagnostic category.

1. Test the engine coolant heater for an open or short to ground. If open or shorted, replace the heater.
2. If the heater tests normal, replace the coolant heater power cord.

Pressure Cap Testing

Tools required

1. J 24460-01 Cooling System Pressure Tester. See «Special Tools»(ref-277850-S19943780362008012100000) .
2. J 42401 Radiator Cap/Surge Tank Test Adapter. See «Special Tools»(ref-277850-S19943780362008012100000) .

1. Remove the pressure cap.
2. Wash the pressure cap sealing surface with water.
3. Use the J 24460-01 (1) with J 42401 (2) in order to test the pressure cap. See «Special Tools»(ref-277850-S19943780362008012100000) .
4. Test the pressure cap for the following conditions: Pressure release when the J 24460-01 exceeds the pressure rating of the pressure cap. See «Special Tools»(ref-277850-S19943780362008012100000) . Maintain the rated pressure for at least 10 seconds. Note the rate of pressure loss.
5. Replace the pressure cap under the following conditions: The pressure cap does not release pressure which exceeds the rated pressure of the cap. The pressure cap does not hold the rated pressure.

Cooling System Leak Testing

Tools Required

1. J 24460-01 Cooling System Pressure Tester. See «Special Tools»(ref-277850-S19943780362008012100000) .
2. J 42401 Radiator Cap/Surge Tank Test Adapter. See «Special Tools»(ref-277850-S19943780362008012100000) .

1. Remove the pressure cap.
2. Test the operation of the pressure cap. Refer to «Pressure Cap Testing»(ref-277850-S36316559412008012100000) .
3. Wash the pressure cap mating surface with water.
4. Use the J 24460-01 with the. See «Special Tools»(ref-277850-S19943780362008012100000) . J 42401 in order to apply pressure to the cooling system. See «Special Tools»(ref-277850-S19943780362008012100000) . Do not exceed the pressure cap rating.
5. The cooling system should hold the rated pressure for at least 2 minutes. Observe the gage for any pressure loss.
6. Repair any leaks as required.

Fan Clutch Diagnosis

Fan Clutch Diagnosis

Inspection Procedure

1. Inspect the thermostats for sticking, cracks, and/or leakage of wax.
2. Replace the thermostats if damage is found.
3. Clean the thermostat housing and thermostat housing cover sealing surfaces.