Hummer H2. Manual - part 25

ENGINE MECHANICAL 

COOLING SYSTEM TROUBLE SHOOTING 

COOLING SYSTEM TROUBLE SHOOTING 

Uneven pad wear caused by caliper 

See DISC BRAKES or BRAKE SYSTEM 

Uneven rotor wear 

See DISC BRAKES or BRAKE SYSTEM 

Drums out-of-round 

Reface or replace drums 

NOTE:

This is GENERAL information. This article is not intended to be specific to any 
unique situation or individual vehicle configuration. The purpose of this Trouble 
Shooting information is to provide a list of common causes to problem 
symptoms. For model-specific Trouble Shooting, refer to SUBJECT, 
DIAGNOSTIC, or TESTING articles available in the section(s) you are accessing. 

CONDITION & POSSIBLE CAUSE 

CORRECTION 

Overheating 

Coolant Leak 

Fill/Pressure Test System 

A/C Condenser Fins Clogged 

Remove/Clean Condenser 

Radiator Fins Clogged 

Remove/Clean Radiator 

Thermostat Stuck Closed 

Replace Thermostat 

Clogged Cooling System Passages 

Clean/Flush Cooling System 

Water Pump Malfunction 

Replace Water Pump 

Fan Clutch Malfunction 

Replace Fan Clutch 

Retarded Ignition Timing 

Reset Ignition Timing 

Cooling Fan Malfunction 

Test Cooling Fan/Circuit 

Cooling Fan Motor Malfunction 

Test Fan Motor 

Cooling Fan Relay Malfunction 

Test Fan Relay 

Faulty Radiator Cap 

Replace Radiator Cap 

Broken/Slipping Fan Belt 

Replace Fan Belt 

Restricted Exhaust 

Repair Exhaust System 

Corrosion 

Impurities In Coolant 

Clean/Flush System 

Coolant Leakage 

Damaged hose 

Replace Hose 

Leaky Water Pump 

Replace Water Pump 

Damaged Radiator Seam 

Replace/Repair Radiator 

Leaky Thermostat Cover 

Replace Thermostat Cover 

Cylinder Head Problem 

Check Head/Head Gasket 

Leaky Freeze Plugs 

Replace Freeze Plugs 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Trouble Shooting - Basic Procedures

  

GASOLINE ENGINE - MECHANICAL TROUBLE SHOOTING 

BASIC GASOLINE ENGINE - MECHANICAL TROUBLE SHOOTING CHART 

Recovery System Inoperative 

Loose and/or Defective Radiator Cap 

Replace Radiator Cap 

Overflow Tube Clogged and/or Leaking 

Repair Tube 

Recovery Bottle Vent Restricted 

Clean Vent 

No Heater Core Flow 

Collapsed Heater Hose 

Replace Heater Hose 

Plugged Heater Core 

Clean/Replace Heater Core 

Faulty Heater Valve 

Replace Heater Valve 

NOTE:

This is GENERAL information. This article is not intended to be specific to any 
unique situation or individual vehicle configuration. The purpose of this Trouble 
Shooting information is to provide a list of common causes to problem 
symptoms. For model-specific Trouble Shooting, refer to SUBJECT, 
DIAGNOSTIC, or TESTING articles available in the section(s) you are accessing. 

CONDITION & POSSIBLE CAUSE 

CORRECTION 

Engine Lopes At Idle 

Intake manifold-to-head leaks 

Replace manifold gasket, See ENGINES 

Blown head gasket 

Replace head gasket, See ENGINES 

Worn timing gears, chain or sprocket 

Replace gears, chain or sprocket 

Worn camshaft lobes 

Replace camshaft, See ENGINES 

Overheated engine 

Check cooling system, See COOLING 

Blocked crankcase vent valve 

Remove restriction 

Leaking EGR valve 

Repair leak and/or replace valve 

Faulty fuel pump 

Replace fuel pump 

Engine Has Low Power 

Leaking fuel pump 

Repair leak and/or replace fuel pump 

Excessive piston-to-bore clearance 

Install larger pistons, See ENGINES 

Sticking valves or weak valve springs 

Check valve train components, See 

ENGINES 

Incorrect valve timing 

Reset valve timing, See ENGINES 

Worn camshaft lobes 

Replace camshaft, See ENGINES 

Blown head gasket 

Replace head gasket. See ENGINES. 

Clutch slipping 

Adjust pedal and/or replace components, See 

ENGINES 

Engine overheating 

Check cooling system, See COOLING 

Auto. Trans. pressure regulator valve 
faulty 

Replace pressure regulator valve 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Trouble Shooting - Basic Procedures

  

Auto. Trans. fluid level too low 

Add fluid as necessary 

Improper vacuum diverter valve 
operation 

Replace vacuum diverter valve 

Vacuum leaks 

Inspect vacuum system and repair as 

required 

Leaking piston rings 

Replace piston rings, See ENGINES 

Faulty High Speed Operation 

Low fuel pump volume 

Replace fuel pump 

Leaking valves or worn 

Replace valves and/or springs, See 

ENGINES 

Incorrect valve timing 

Reset valve timing,See ENGINES 

Intake manifold restricted 

Remove restriction 

Worn distributor shaft 

Replace distributor 

Faulty Acceleration 

Improper fuel pump stroke 

Remove pump and reset pump stroke 

Incorrect ignition timing 

Reset ignition timing, See TUNE-UP 

Leaking valves 

Replace valves, See ENGINES 

Worn fuel pump diaphragm or piston 

Replace diaphragm or piston 

Intake Backfire 

Improper ignition timing 

Reset ignition timing, See TUNE-UP 

Faulty accelerator pump discharge 

Replace accelerator pump 

Improper choke operation 

Check choke and adjust as required 

Defective EGR valve 

Replace EGR valve 

Fuel mixture too lean 

Reset air/fuel mixture, See TUNE-UP 

Choke valve initial clearance too large 

Reset choke valve initial clearance 

Exhaust Backfire 

Vacuum leak 

Inspect and repair vacuum system 

Faulty vacuum diverter valve 

Replace vacuum diverter valve 

Faulty choke operation 

Check choke and adjust as required 

Exhaust system leak 

repair exhaust system leak 

Engine Detonation 

Ignition timing too far advanced 

Reset ignition timing, See TUNE-UP 

Faulty ignition system 

Check ignition timing, See TUNE-UP 

Spark plugs loose or faulty 

Retighten or replace plugs 

Fuel delivery system clogged 

Inspect lines, pump and filter for clog 

EGR valve inoperative 

Replace EGR valve 

PCV system inoperative 

Inspect and/or replace hoses or valve 

Vacuum leaks 

Check vacuum system and repair leaks 

Excessive combustion chamber deposits 

Remove built-up deposits 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Trouble Shooting - Basic Procedures

  

Leaking, sticking or broken valves 

Inspect and/or replace valves 

External Oil Leakage 

Fuel pump improperly seated or worn 
gasket 

Remove pump, replace gasket and seat 

properly 

Oil pan gasket broken or pan bent 

Straighten pan and replace gasket 

Timing chain cover gasket broken 

Replace timing chain cover gasket 

Rear main oil seal worn 

Replace rear main oil seal 

Oil pan drain plug not seated properly 

Remove and reinstall drain plug 

Camshaft bearing drain hole blocked 

Remove restriction 

Oil pressure sending switch leaking 

Remove and reinstall sending switch 

Excessive Oil Consumption 

Worn valve stems or guides 

Replace stems or guides, See ENGINES 

Valve "O" ring seals damaged 

Replace "O" ring seals, See ENGINES 

Plugged oil drain back holes 

Remove restrictions 

Improper PCV valve operation 

Replace PCV valve 

Engine oil level too high 

Remove excess oil 

Engine oil too thin 

Replace thicker oil 

Valve stem oil deflectors damaged 

Replace oil deflectors 

Incorrect piston rings 

Replace piston rings, See ENGINES 

Piston ring gaps not staggered 

Reinstall piston rings, See ENGINES 

Insufficient piston ring tension 

Replace rings, See ENGINES 

Piston ring grooves or oil return 

slots clogged Replace piston rings, See 

ENGINES 

Piston rings sticking in grooves 

Replace piston rings, See ENGINES 

Piston ring grooves excessively worn 

Replace piston and rings, See ENGINES 

Compression rings installed upside 
down 

Replace compression rings correctly, See 

ENGINES 

Worn or scored cylinder walls 

Rebore cylinders or replace block 

Mismatched oil ring expander and rail 

Replace oil ring expander and rail, See 

ENGINES 

Intake gasket dowels too long 

Replace intake gasket dowels 

Excessive main or connecting rod 
bearing clearance 

Replace main or connecting rod bearings, 

See ENGINES 

No Oil Pressure 

Low oil level 

Add oil to proper level 

Oil pressure sender or gauge broken 

Replace sender or gauge 

Oil pump malfunction 

Remove and overhaul oil pump, See 

ENGINES 

Oil pressure relief valve sticking 

Remove and reinstall valve 

Oil pump passages blocked 

Overhaul oil pump, See ENGINES 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Trouble Shooting - Basic Procedures