Engine Cooling System: Diagnosis Cadillac STS I

Diagnostic Starting Point - Engine Cooling

Begin the system diagnosis with the Diagnostic System Check - Vehicle in Vehicle DTC Information. 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

Engine Control Module (ECM) Scan Tool Output Controls

HVAC Control Module Scan Tool Output Controls

Scan Tool Data List

Scan Tool Data List

Circuit Description

The engine control module (ECM) 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 ECM 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 ECM is commanding a fan relay ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding a fan relay OFF, the voltage potential of the control circuit should be high, near battery voltage.

The ECM monitors the relay control circuits for the following conditions

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

If the ECM detects an improper voltage level on the low or high speed driver circuits, then code P0480, P0481, P0691, P0692, P0693, or P0694, 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
3. DTC P0691 Cooling Fan Relay 1 Control Circuit Low Voltage
4. DTC P0692 Cooling Fan Relay 1 Control Circuit High Voltage
5. DTC P0693 Cooling Fan Relay 2 Control Circuit Low Voltage
6. DTC P0694 Cooling Fan Relay 2 Control Circuit High Voltage

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 ECM detects an open circuit on the high speed cooling fan relay control circuit.
2. P0693 -The ECM detects a short to ground on the high speed cooling fan relay control circuit.
3. P0694 -The ECM detects a short to voltage on the high speed cooling fan relay control circuit.
4. P0480 -The ECM detects an open on the low speed cooling fan relay control circuit.
5. P0691 -The ECM detects a short to ground on the low speed cooling fan relay control circuit.
6. P0692 -The ECM detects a short to voltage on the low speed cooling fan relay control circuit.
7. The above condition is present for one second.

Action Taken When the DTC Sets

1. The ECM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
2. The ECM 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 ECM 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-197533-S35858719362005101200000) in Wiring Systems.
2. Review the Freeze/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 engine control module (ECM) uses the engine coolant temperature (ECT) sensor to monitor the engine for an over temperature condition. This condition occurs when the coolant temperature is above 131°C (268°F). When an over temperature condition is present, DTC P1258 will set. The ECM will disable 2 groups of 4 cylinders by turning OFF the fuel injectors. By switching between the 2 groups of cylinders, the ECM 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

The ignition is ON.

1. The ECM detects an ECT over 131°C (268°F).
2. The above condition is present for at least 3 seconds.

1. The ECM will illuminate the malfunction indicator lamp (MIL) during the first trip in which the diagnostic test has been run and failed.
2. The ECM will signal the instrument panel cluster (IPC) to turn ON the Service Engine Soon indicator.
3. The ECM will alternately disable 2 groups of 4 cylinders by turning OFF the fuel injectors.
4. The ECM will store conditions which were present when the DTC set in Freeze Frame Data.
5. The ECM will command the fan on high speed.

1. The ECM 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-197533-S03944243902005101200000) in Wiring Systems.
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. «Low Engine Coolant Indicator Always On»(ref-197587-S18069068562005101200000)
2. «Cooling Fan Always On»(ref-197587-S42172399022005101200000)
3. «Cooling Fan Inoperative»(ref-197587-S08202705042005101200000)
4. «Engine Overheating»(ref-197587-S08374119362005101200000)
5. «Loss of Coolant»(ref-197587-S01695883312005101200000)
6. «Thermostat Diagnosis»(ref-197587-S38506262092005101200000)
7. «Engine Fails To Reach Normal Operating Temperature»(ref-197587-S31615076532005101200000)
8. «Pressure Cap Testing»(ref-197587-S13114354272005101200000)
9. «Cooling System Leak Testing»(ref-197587-S13137700512005101200000)

The engine may overheat due to an intermittent operation of one of the following components

1. The after boil heater pump
2. The coolant bypass solenoid
3. The coolant bypass valve
4. The mechanical cooling fan
5. The electric cooling fans
6. The thermostat

For electrical inspection of the cooling fans and the after boil heater pump, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Engine Overheating

The engine may fail to reach normal operating temperature due to an intermittent operation of one of the following components

1. The thermostat
2. The electric fan system
3. The mechanical fan system

For electrical inspection of the electrical fan system, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

For mechanical fan system inspection, refer to Fan Clutch Diagnosis .

Engine Fails To Reach Normal Operating Temperature

Pressure Cap Testing

Tools Required

1. J 24460-01 Cooling System Pressure Tester. See «Special Tools»(ref-197587-S04508623182005101200000) .
2. J 42401 Radiator Cap/Surge Tank Test Adapter. See «Special Tools»(ref-197587-S04508623182005101200000) .

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-197587-S04508623182005101200000) .
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-197587-S04508623182005101200000) . 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-197587-S04508623182005101200000) .
2. J 42401 Radiator Cap/Surge Tank Test Adapter. See «Special Tools»(ref-197587-S04508623182005101200000) .

1. Remove the pressure cap.
2. Test the operation of the pressure cap. Refer to «Pressure Cap Testing»(ref-197587-S13114354272005101200000) .
3. Wash the pressure cap mating surface with water.
4. Use the J 24460-01 (1) with J 42401 (2) in order to apply pressure to the cooling system. See «Special Tools»(ref-197587-S04508623182005101200000) . 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