Hummer H2. Manual - part 28
Low fuel pressure
Test pressure regulator and fuel pump, check for
restricted lines and filters
No distributor reference
pulses
Repair ignition system as necessary
Open coolant temperature
sensor circuit
Test sensor and wiring
Shorted W.O.T. switch in
T.P.S.
Disconnect W.O.T. switch, engine should start
Defective ECM
Replace ECM
Fuel tank residual pressure
valve leaks
Test for fuel pressure drop after shut down
Hard Starting
Disconnected hot air tube to
air cleaner
Reconnect tube and test control valve
Defective Idle Air Control
(IAC) valve
Test valve operation and circuit
Shorted, open or misadjusted
T.P.S.
Test and adjust or replace T.P.S.
EGR valve open
Test EGR valve and control circuit
Poor Oxygen sensor signal
Test for shorted or circuit
Incorrect mixture from PCV
system
Test PCV for flow, check sealing of oil filter cap
Poor High Speed Operation
Low fuel pump volume
Faulty pump or restricted fuel lines or filters
Poor MAP sensor signal
Test MAP sensor, vacuum hose and wiring
Poor Oxygen sensor signal
Test for shorted or open sensor or circuit
Open coolant temperature
sensor circuit
Test sensor and wiring
Faulty ignition operation
Check wires for cracks or poor con- nections, test
secondary voltage with oscilloscope
Contaminated fuel
Test fuel for water or alcohol
Intermittent ECM ground
Test ECM ground connection for resistance
Restricted air cleaner
Replace air cleaner
Restricted exhaust system
Test for exhaust manifold back pressure
Poor MAF sensor signal
Check leakage between sensor and manifold
Poor VSS signal
If tester for ALCL hook-up is available check that
VSS reading matches speedometer
Ping or Knock on Acceleration
Poor Knock sensor signal
Test for shorted or open sensor or circuit
Poor Baro sensor signal
Test for shorted or open sensor or circuit
Improper ignition timing
See VEHICLE EMISSION CONTROL LABEL
1998 Chevrolet Pickup C1500
GENERAL INFORMATION Trouble Shooting - Basic Procedures