5B.36
Section 5B
EFI Fuel System
Diagnostic Aid #5 “FUEL PUMP” (fuel pump not
turning on)
Possible causes:
1. Fuel pump fuse
2. Fuel pump circuit problem. Circuits 30, 87, and
relay.
3. Fuel pump
Diagnostic Aid #6 “RELAY” (relay not operating)
Possible causes:
1. Safety switches/circuit(s) problem. Circuit 25.
2. Relay circuit(s) problem. Circuits 28, 85, 30, and
87.
3. Relay
4. ECU grounds
5. ECU
Diagnostic Aid #7 “IGNITION SYSTEM” (no spark)
Possible causes:
1. Spark plug
2. Plug wire
3. Coil
4. Coil circuit(s). Circuits 30, 31, 65, 66, relay and
relay circuit 30.
5. ECU grounds
6. ECU
Diagnostic Aid #8 “FUEL SYSTEM-ELECTRICAL”
(no fuel delivery)
Possible causes:
1. No fuel
2. Air in fuel rail
3. Fuel valve shut off
4. Fuel filter/line plugged
5. Injector circuit(s). Circuits 14, 15, 45 and 4A.
6. Injector
7. ECU grounds
8. ECU
Diagnostic Aid #9 “FUEL SYSTEM” (fuel pressure)
Possible causes for low fuel system pressure:
1. Low fuel
2. Fuel filter plugged
3. Fuel supply line plugged
4. Pressure regulator
5. Fuel pump
Possible causes for high fuel system pressure:
1. Pressure regulator
2. Fuel return line plugged or restricted.
Diagnostic Aid #10 “BASIC ENGINE” (cranks but will
not run)
Possible causes:
1. Refer to basic engine troubleshooting charts within
service manual sections 3, 5, and 8.
Common Complaints/Problems
Following are some of the most common complaints or
problems reported by customers. For each problem,
you will find a list of the most likely causes or areas to
be investigated. Always start by checking if there are
any stored fault codes to guide you in the right
direction.
Engine starts hard or fails to start when cold. (Code
31, 42, 51, 52, 56)
1. Fuel pump or relay, not activating/operational.
2. Engine (Coolant) Temperature sensor faulty.
3. Fuel pressure insufficient/incorrect.
4. Fuel injector(s) leaking.
5. Fuel injector(s), fuel filter, fuel line, or fuel
pick-up dirty, clogged, or restricted.
6. Speed sensor malfunction.
7. Stale fuel.
8. Low system voltage.
9. Bad spark plug(s) or coil(s).
10. Base ignition timing incorrect.
Engine starts hard or fails to start when warm.
(Code 42, 51, 52)
1. Insufficient fuel system pressure.
2. Engine (Coolant) Temperature sensor faulty.
3. Fuel injector(s) leaking.
4. Fuel injector(s), fuel filter, fuel line, or fuel pick-up
dirty/restricted.
5. Low fuel pressure.
6. Wrong grade of fuel.
7. Bad spark plug(s) or coil(s).
8. Low system voltage.
9. Speed sensor problem.
10. Base ignition timing problem.
Engine stalls or idles roughly. (Code 22, 31, 34, 42,
43, 51, 52)
1. Vacuum (intake air) leak.
2. Fuel injector(s), fuel filter, fuel line, or fuel pick-up
dirty/clogged/restricted.
3. Insufficient fuel pressure/delivery.
4. Engine (Coolant) Temperature sensor faulty.
5. TPS faulty or “TPS Initialization Procedure”
incorrect.
6. Leaking fuel injector O-Rings.
7. Bad spark plug(s) or coil(s).
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