DIAGNOSIS AND TESTING
ON-BOARD DIAGNOSTICS (OBD)
COOLING SYSTEM RELATED DIAGNOSTICS
The powertrain control module (PCM) has been programmed to monitor certain cooling system components:
- If the engine has remained cool for too long a period, such as with a stuck open thermostat, a Diagnostic Trouble Code (DTC) can be set.
- If an open or shorted condition has developed in the relay circuit controlling the electric radiator fan or fan control solenoid circuit controlling the hydraulic fan, a Diagnostic Trouble Code (DTC) can be set.
If the problem is sensed in a monitored circuit often enough to indicated an actual problem, a DTC is stored. The DTC will be stored in the PCM memory for eventual display to the service technician. (Refer to 25 - EMISSIONS CONTROL - DESCRIPTION).
ACCESSING DIAGNOSTIC TROUBLE CODES
To read DTC's and to obtain cooling system data, (Refer to 25 - EMISSIONS CONTROL - DESCRIPTION).
ERASING TROUBLE CODES
After the problem has been repaired, use the scan tool to erase a DTC. Refer to the appropriate Powertrain Diagnostic Procedures service information for operation of the scan tool.
PRELIMINARY CHECKS
ENGINE COOLING SYSTEM OVERHEATING
Establish what driving conditions caused the complaint. Abnormal loads on the cooling system such as the following may be the cause:
- Prolonged idle
- Very high ambient temperature
- Slight tail wind at idle
- Slow traffic
- Traffic jams
- High speed
- Trailer towing
- Steep grades
- Any accessory addition that fully or partially blocks the grille opening
Driving techniques that avoid overheating are:
- Idle with A/C off when temperature gauge is at end of normal range.
- Increase engine speed for more air flow is recommended.
1. TRAILER TOWING:
Consult Trailer Towing section of owners manual. Do not exceed limits.
2. RECENT SERVICE OR ACCIDENT REPAIR:
Determine if any recent service has been performed on vehicle that may effect cooling system. This may be:
- Engine adjustments (incorrect timing)
- Slipping engine accessory drive belt(s)
- Brakes (possibly dragging)
- Changed parts. Incorrect water pump, or pump rotating in wrong direction due to belt not correctly routed
- Reconditioned radiator or cooling system refilling (possibly under filled or air trapped in system).
NOTE: If investigation reveals none of the previous items as a cause for an engine overheating complaint, refer to following Cooling System Diagnosis charts.
These charts are to be used as a quick-reference only. Refer to the group text for information.
| CONDITION | POSSIBLE CAUSES | CORRECTION |
| TEMPERATURE GAUGE READS LOW | 1. Has a Diagnostic Trouble Code (DTC) been set indicating a stuck open thermostat? | 1. Refer to
(Refer to 25 - EMISSIONS CONTROL - DESCRIPTION) for On-Board Diagnostics and DTC information.
Replace thermostat if necessary. |
| 2. Is the temperature sending unit connected? | 2. Check the temperature sensor connector.
(Refer to 7 - COOLING/ENGINE/ENGINE COOLANT TEMP SENSOR -
DESCRIPTION). Repair connector if necessary. | |
| 3. Is the temperature gauge operating OK? | 3. Check gauge operation. Repair as necessary. | |
| 4. Coolant level low in cold ambient temperatures accompanied with poor heater performance. | 4. Check coolant level in the coolant reserve/overflow tank and the radiator. Inspect system for leaks. Repair leaks as necessary. | |
| 5. Improper operation of internal heater doors or heater controls. | 5. Inspect heater and repair as necessary.
(Refer to 24 - HEATING & AIR CONDITIONING - DIAGNOSIS
AND TESTING) | |
| TEMPERATURE GAUGE READS HIGH OR THE COOLANT LAMP ILLUMINATES. COOLANT MAY OR MAY NOT BE LOST OR LEAKING FROM THE COOLING SYSTEM | 1. Trailer is being towed, a steep hill is being climbed, vehicle is operated in slow moving traffic, or engine is being idled with very high ambient (outside) temperatures
and the air conditioning is on. Higher altitudes could aggravate these conditions. | 1. This may be a temporary condition and repair is not necessary. Turn off the air conditioning and attempt to drive the vehicle without any of the previous conditions.
Observe the temperature gauge. The gauge should return to the normal range. If the gauge does not return to the normal range, determine the cause for overheating and repair. |
| 2. Is the temperature gauge reading correctly? | 2. Check gauge. (Refer to Group 8J - INSTRUMENT CLUSTER). Repair as necessary. | |
| 3. Is the temperature warning illuminating unnecessarily? | 3. Check warning lamp operation. (Refer to Group 8J - INSTRUMENT CLUSTER). Repair as necessary. | |
| 4. Coolant low in coolant reserve/overflow tank and radiator? | 4. Check for coolant leaks and repair as necessary.
(Refer to 7 - COOLING - DIAGNOSIS AND TESTING). | |
| 5. Pressure cap not installed tightly. If cap is loose, boiling point of coolant will be lowered. Also refer to the following Step 6. | 5. Tighten cap | |
| 6. Poor seals at the radiator cap. | 6. (a) Check condition of cap and cap seals.
(Refer to 7 - COOLING/ENGINE/RADIATOR PRESSURE CAP - DIAGNOSIS
AND TESTING). | |
| (b) Check condition of radiator filler neck. If neck is bent or damaged, replace radiator. | ||
| 7. Coolant level low in radiator but not in coolant reserve/overflow tank. This means the radiator is not drawing coolant from the coolant reserve/overflow
tank as the engine cools | 7. (a) Check condition of radiator cap and cap seals.
(Refer to 7 - COOLING/ENGINE/RADIATOR PRESSURE
CAP - DIAGNOSIS AND TESTING). | |
| (b) Check condition of radiator filler neck. If neck is bent or damaged, replace radiator. | ||
| (c) Check condition of the hose from the radiator to the coolant tank. It should fit tight at both ends without any kinks or tears. Replace hose if necessary. | ||
| (d) Check coolant reserve/overflow tank and tanks hoses for blockage. Repair as necessary. | ||
| 8. Incorrect coolant concentration | 8. Check coolant.
(Refer to 7 - COOLING/ENGINE/COOLANT - DESCRIPTION) for correct coolant/water mixture
ratio. | |
| 9. Coolant not flowing through system | 9. Check for coolant flow at radiator filler neck with some coolant removed, engine warm and thermostat open. Coolant should be observed flowing through radiator.
If flow is not observed, determine area of obstruction and repair as necessary. | |
| 10. Radiator or A/C condenser fins are dirty or clogged. | 10. Remove insects and debris.
(Refer to 7 - COOLING/ENGINE/RADIATOR - CLEANING). | |
| 11. Radiator core is corroded or plugged. | 11. Have radiator re-cored or replaced. | |
| 12. Aftermarket A/C installed without proper radiator. | 12. Install proper radiator. | |
| 13. Fuel or ignition system problems. | 13. Refer to FUEL and /or IGNITION CONTROL for diagnosis. | |
| 14. Dragging brakes. | 14. Check and correct as necessary.
(Refer to 5 - BRAKES - DIAGNOSIS AND TESTING) for correct procedures. | |
| 15. Bug screen or cardboard is being used, reducing airflow. | 15. Remove bug screen or cardboard. | |
| 16. Thermostat partially or completely shut. | 16. Check thermostat operation and replaces necessary.
(Refer to 7 - COOLING/ENGINE/ENGINE COOLANT THERMOSTAT
- DIAGNOSIS AND TESTING). | |
| 17. Viscous fan drive not operating properly. | 17. Check fan drive operation and replace as necessary.
(Refer to 7 - COOLING/ENGINE/FAN DRIVE VISCOUS
CLUTCH - DIAGNOSIS AND TESTING). | |
| 18. Cylinder head gasket leaking. | 18. Check for cylinder head gasket leaks.
(Refer to 7 - COOLING - DIAGNOSIS AND TESTING). For repair,
(Refer to 9 - ENGINE/CYLINDER HEAD - REMOVAL). | |
| 19. Heater core leaking. | 19. Check heater core for leaks.
(Refer to 24 - HEATING & AIR CONDITIONING/PLUMBING/HEATER CORE -
REMOVAL). Repair as necessary. | |
| 20. Hydraulic fan speed too low or inoperative. | 20. Check for DTC code. Check fan operation speeds. Refer to fan speed operation table. Low power steering pump output. Refer to power steering pump diagnosis - 4.7L engine. | |
| TEMPERATURE GAUGE READING IS INCONSISTENT (FLUCTUATES, CYCLES OR IS ERRATIC) | 1. During cold weather operation, with the heater blower in the high position, the gauge reading may drop slightly. | 1. A normal condition. No correction is necessary. |
| 2. Temperature gauge or engine mounted gauge sensor defective or shorted. Also, corroded or loose wiring in this circuit. | 2. Check operation of gauge and repair if necessary. Refer to Group 8J, Instrument cluster. | |
| 3. Gauge reading rises when vehicle is brought to a stop after heavy use (engine still running) | 3. A normal condition. No correction is necessary. Gauge should return to normal range after vehicle is driven. | |
| 4. Gauge reading high after re-starting a warmed up (hot) engine. | 4. A normal condition. No correction is necessary. The gauge should return to normal range after a few minutes of engine operation. | |
| 5. Coolant level low in radiator (air will build up in the cooling system causing the thermostat to open late). | 5. Check and correct coolant leaks.
(Refer to 7 - COOLING - DIAGNOSIS AND TESTING). | |
| 6. Cylinder head gasket leaking allowing exhaust gas to enter cooling system causing a thermostat to open late. | 6. (a) Check for cylinder head gasket leaks.
(Refer to 7 - COOLING - DIAGNOSIS AND TESTING). | |
| (b) Check for coolant in the engine oil. Inspect for white steam emitting from the exhaust system. Repair as necessary. | ||
| 7. Water pump impeller loose on shaft. | 7. Check water pump and replace as necessary.
(Refer to 7 - COOLING/ENGINE/WATER PUMP - DIAGNOSIS AND
TESTING) . | |
| 8. Loose accessory drive belt. (water pump slipping) | 8.
(Refer to 7 - COOLING/ACCESSORY DRIVE/DRIVE BELTS - DIAGNOSIS AND TESTING) . Check and correct as
necessary. | |
| 9. Air leak on the suction side of the water pump allows air to build up in cooling system causing thermostat to open late. | 9. Locate leak and repair as necessary. | |
| PRESSURE CAP IS BLOWING OFF STEAM AND/OR COOLANT TO COOLANT TANK. TEMPERATURE GAUGE READING MAY BE ABOVE NORMAL BUT NOT HIGH. COOLANT LEVEL MAY BE HIGH IN COOLANT
RESERVE/OVERFLOW TANK | 1. Pressure relief valve in radiator cap is defective. | 1. Check condition of radiator cap and cap seals.
(Refer to 7 - COOLING/ENGINE/RADIATOR PRESSURE CAP
- DIAGNOSIS AND TESTING). Replace cap as necessary. |
| COOLANT LOSS TO THE GROUND WITHOUT PRESSURE CAP BLOWOFF. GAUGE READING HIGH OR HOT | 1. Coolant leaks in radiator, cooling system hoses, water pump or engine. | 1. Pressure test and repair as necessary.
(Refer to 7 - COOLING - DIAGNOSIS AND TESTING). |
| DETONATION OR PRE-IGNITION (NOT CAUSED BY IGNITION SYSTEM). GAUGE MAY OR MAY NOT BE READING HIGH | 1. Engine overheating. | 1. Check reason for overheating and repair as necessary. |
| 2. Freeze point of coolant not correct. Mixture is too rich or too lean. | 2. Check coolant concentration.
(Refer to 7 - COOLING/ENGINE/COOLANT - DESCRIPTION) and adjust ratio
as required. | |
| HOSE OR HOSES COLLAPSE WHILE ENGINE IS RUNNING | 1. Vacuum created in cooling system on engine cool-down is not being relieved through coolant reserve/overflow system. | 1. (a) Radiator cap relief valve stuck.
(Refer to 7 - COOLING/ENGINE/RADIATOR PRESSURE CAP
- DIAGNOSIS AND TESTING). Replace if necessary |
| (b) Hose between coolant reserve/overflow tank and radiator is kinked. Repair as necessary. | ||
| (c) Vent at coolant reserve/overflow tank is plugged. Clean vent and repair as necessary. | ||
| (d) Reserve/overflow tank is internally blocked or plugged. Check for blockage and repair as necessary. | ||
| NOISY VISCOUS FAN/DRIVE | 1. Fan blades loose - 4.7L. | 1. Replace fan blade assembly.
(Refer to 7 - COOLING/ENGINE/RADIATOR FAN - REMOVAL) |
| 2. Fan blades striking a surrounding object. | 2. Locate point of fan blade contact and repair as necessary. | |
| 3. Air obstructions at radiator or air conditioning condenser. | 3. Remove obstructions and/or clean debris or insects from radiator or A/C condenser. | |
| 4. Thermal viscous fan drive has defective bearing - 4.7L | 4. Replace fan drive. Bearing is not serviceable.
(Refer to 7 - COOLING/ENGINE/RADIATOR FAN - REMOVAL). | |
| INADEQUATE HEATER PERFORMANCE. | 1.Thermostat failed in open position | 1. Check thermostat operation and replaces necessary
(Refer to 7 - COOLING/ENGINE/ENGINE COOLANT THERMOSTAT
- DIAGNOSIS AND TESTING) |
| 2. Has a Diagnostic trouble Code (DTC) been set? | 2.
(Refer to 25 - EMISSIONS CONTROL - DESCRIPTION) for correct procedures and replace thermostat if
necessary | |
| 3. Coolant level low | 3.
(Refer to 7 - COOLING - DIAGNOSIS AND TESTING). | |
| 4. Obstructions in heater hose/fittings | 4. Remove heater hoses at both ends and check for obstructions | |
| 5. Heater hose kinked | 5. Locate kinked area and repair as necessary | |
| 6. Water pump is not pumping water to/through the heater core. When the engine is fully warmed up, both heater hoses should be hot to the touch. If only one of the
hoses is hot, the water pump may not be operating correctly or the heater core may be plugged. Accessory drive belt may be slipping causing poor water pump operation. | 6.
(Refer to 7 - COOLING/ENGINE/WATER PUMP - DIAGNOSIS AND TESTING). If a slipping belt is detected,
(Refer to 7 - COOLING/ACCESSORY DRIVE/DRIVE BELTS - REMOVAL). If heater core obstruction is detected,
(Refer
to 7 - COOLING - STANDARD PROCEDURE) for cooling system reverse flushing. | |
| STEAM IS COMING FROM THE FRONT OF VEHICLE NEAR THE GRILL AREA WHEN WEATHER IS WET, ENGINE IS WARMED UP AND RUNNING, AND VEHICLE IS STATIONARY. TEMPERATURE GAUGE IS
IN NORMAL RANGE | 1. During wet weather, moisture (snow, ice or rain condensation) on the radiator will evaporate when the thermostat opens. This opening allows heated water into the
radiator. When the moisture contacts the hot radiator, steam may be emitted. This usually occurs in cold weather with no fan or airflow to blow it away. | 1. Occasional steam emitting from this area is normal. No repair is necessary. |
| COOLANT COLOR | 1. Coolant color is not necessarily an indication of adequate corrosion or temperature protection. Do not rely on coolant color for determining condition of coolant. | 1.
(Refer to 7 - COOLING/ENGINE/COOLANT - DESCRIPTION) for coolant concentration information. Adjust
coolant mixture as necessary. |
| COOLANT LEVEL CHANGES IN COOLANT RESERVE/OVERFLOW TANK. TEMPERATURE GAUGE IS IN NORMAL RANGE | 1. Level changes are to be expected as coolant volume fluctuates with engine temperature. If the level in the tank was between the FULL and ADD marks at normal operating
temperature, the level should return to within that range after operation at elevated temperatures. | 1. A normal condition. No repair is necessary. |
| FAN RUNS ALL THE TIME | 1. Fan control sensors inoperative. | 1. Check for DTC's. Verify sensor readings. |
| 2. Fan control solenoid stuck "on". | 2. Check fan operation speeds. Refer to fan speed operation table. | |
| 3. Fan control solenoid harness damaged. | 3. Check for DTC 1499. Repair as required. | |
| 4. Transmission temperature too high. | 4. Check for transmission over temp. DTC. | |
| 5. Engine coolant temperature too high. | 5. (a) Check coolant level. Correct level as required. | |
| (b) Thermostat stuck. Replace thermostat. | ||
| (c) Water pump failed. Replace water pump. | ||
| (d) Coolant flow restricted. Clean radiator. | ||
| (e) Air flow over radiator obstructed. Remove obstruction. |
COOLING SYSTEM LEAKS
ULTRAVIOLET LIGHT METHOD
A leak detection additive is available through the parts department that can be added to cooling system. The additive is highly visible under ultraviolet light (black light). Pour one ounce of additive into cooling system. Place heater control unit in HEAT position. Start and operate engine until radiator upper hose is warm to touch. Aim the commercially available black light tool at components to be checked. If leaks are present, black light will cause additive to glow a bright green color.
The black light can be used in conjunction with a pressure tester to determine if any external leaks exist .
PRESSURE TESTER METHOD
The engine should be at normal operating temperature. Recheck the system cold if cause of coolant loss is not located during the warm engine examination.
WARNING: Hot, pressurized coolant can cause injury by scalding.
Carefully remove radiator pressure cap from filler neck and check coolant level. Push down on cap to disengage it from stop tabs. Wipe inside of filler neck and examine lower inside sealing seat for nicks, cracks, paint, dirt and solder residue. Inspect radiator-to- reserve/overflow tank hose for internal obstructions. Insert a wire through the hose to be sure it is not obstructed.
Inspect cams on outside of filler neck. If cams are damaged, seating of pressure cap valve and tester seal will be affected.
Attach pressure tester (7700 or an equivalent) to radiator filler neck .
Operate tester pump to apply 103.4 kPa (15 psi) pressure to system. If hoses enlarge excessively or bulges while testing, replace as necessary. Observe gauge pointer and determine condition of cooling system according to following criteria:
Holds Steady: If pointer remains steady for two minutes, serious coolant leaks are not present in system. However, there could be an internal leak that does not appear with normal system test pressure. If it is certain that coolant is being lost and leaks cannot be detected, inspect for interior leakage or perform Internal Leakage Test.
Drops Slowly: Indicates a small leak or seepage is occurring. Examine all connections for seepage or slight leakage with a flashlight. Inspect radiator, hoses, gasket edges and heater. Seal small leak holes with a Sealer Lubricant (or equivalent). Repair leak holes and inspect system again with pressure applied.
Drops Quickly: Indicates that serious leakage is occurring. Examine system for external leakage. If leaks are not visible, inspect for internal leakage. Large radiator leak holes should be repaired by a reputable radiator repair shop.
INTERNAL LEAKAGE INSPECTION
Remove engine oil pan drain plug and drain a small amount of engine oil. If coolant is present in the pan, it will drain first because it is heavier than oil. An alternative method is to operate engine for a short period to churn the oil. After this is done, remove engine dipstick and inspect for water globules. Also inspect transmission dipstick for water globules and transmission fluid cooler for leakage.
WARNING: With radiator pressure tester tool installed on radiator, do not allow pressure to exceed 110 kpa (20 psi). Pressure will build up quickly if a combustion leak is present. To release pressure, rock tester from side to side. When removing tester, do not turn tester more than 1/2 turn if system is under pressure.
Operate engine without pressure cap on radiator until thermostat opens. Attach a Pressure Tester to filler neck. If pressure builds up quickly it indicates a combustion leak exists. This is usually the result of a cylinder head gasket leak or crack in engine. Repair as necessary.
If there is not an immediate pressure increase, pump the Pressure Tester. Do this until indicated pressure is within system range of 110 kPa (16 psi). Fluctuation of gauge pointer indicates compression or combustion leakage into cooling system.
Because the vehicle is equipped with a catalytic converter, do not remove spark plug cables or short out cylinders to isolate compression leak.
If the needle on dial of pressure tester does not fluctuate, race engine a few times to check for an abnormal amount of coolant or steam. This would be emitting from exhaust pipe. Coolant or steam from exhaust pipe may indicate a faulty cylinder head gasket, cracked engine cylinder block or cylinder head.
A convenient check for exhaust gas leakage into cooling system is provided by a commercially available Block Leak Check tool. Follow manufacturers instructions when using this product.
COMBUSTION LEAKAGE TEST - WITHOUT PRESSURE TESTER
DO NOT WASTE reusable coolant. If solution is clean, drain coolant into a clean container for reuse.
WARNING: Do not remove cylinder block drain plugs or loosen radiator draincock with system hot and under pressure. Serious burns from coolant can occur.
Drain sufficient coolant to allow thermostat removal. (Refer to 7 - COOLING/ENGINE/ENGINE COOLANT THERMOSTAT - REMOVAL). Remove accessory drive belt (Refer to 7 - COOLING/ACCESSORY DRIVE/DRIVE BELTS - REMOVAL).
Add coolant to radiator to bring level to within 6 mm (1/4 in) of top of thermostat housing.
CAUTION: Avoid overheating. Do not operate engine for an excessive period of time. Open draincock immediately after test to eliminate boil over.
Start engine and accelerate rapidly three times, to approximately 3000 rpm while observing coolant. If internal engine combustion gases are leaking into cooling system, bubbles will appear in coolant. If bubbles do not appear, internal combustion gas leakage is not present.
COOLING SYSTEM DEAERATION
As the engine operates, any air trapped in cooling system gathers under the radiator cap. The next time the engine is operated, thermal expansion of coolant will push any trapped air past radiator cap into the coolant reserve/overflow tank. Here it escapes to the atmosphere into the tank. When the engine cools down the coolant, it will be drawn from the reserve/overflow tank into the radiator to replace any removed air.