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5B.37
Section 5B
EFI Fuel System
5B
3. Fuel Pump Relay Related
a. Bad fuel pump relay.
Primary side functional but pin 30 to pin 87
remains open. Primary side pin 85 to pin 86 is
either open, or shorted during engine
operation. Note: after key-off then key-on,
code 56 would be set also.
4. ECU Related
a. Circuit controlling injector #1 damaged.
b. Circuit controlling fuel pump relay damaged.
Code: 52 “32 Pin” (MSE 1.1) Plastic-
Cased ECU only.
Source: Injector #2 circuit open, shorted to
ground,or shorted to battery.
Explanation: Injector #2 is not functioning because
the circuit is open, shorted to ground,
or shorted to battery.
Expected Engine
Response: Engine will run very poorly with only
one cylinder functioning.
Possible Causes:
1. Injector Related
a. Injector coil shorted or opened.
2. Engine Wiring Harness Related
a. Broken or shorted wire in harness.
ECU pin 15 to injector pin 2.
ECU pin 28 to fuel pump relay pin 86. Note:
after key-off then key-on code 56 would be set
also. Fuel pump relay pin 87 to injector pin 1.
b. Opened main fuse F1.
3. Fuel Pump Relay Related
a. Bad fuel pump relay.
Primary side functional, but pin 30 to pin 87
remains open. Primary side pin 85 to pin 86 is
open or shorted during engine operation.
Note: after key-off then key-on code 56 would
be set also.
4. ECU Related
a. Circuit controlling injector #2 damaged.
b. Circuit controlling fuel pump relay damaged.
Code: 55 “32 Pin” (MSE 1.1) Plastic-
Cased ECU only.
Source: MIL (Diagnostic lamp) circuit open,
shorted to ground, or shorted to
battery.
Explanation: MIL is not functioning because the
circuit is open, shorted to ground, or
shorted to battery.
Expected Engine
Response: Engine will run normally if no other
errors are present.
Possible Causes:
1. MIL (diagnostic lamp) Related
a. MIL element opened or element shorted to
ground.
b. Lamp missing.
2. Engine Wiring Harness Related
a. Broken or shorted wire in harness.
ECU pin 29 to lamp open or shorted.
3. Vehicle Wiring Harness Related
a. Broken or shorted wire in harness.
Power lead to MIL open or shorted.
4. ECU related
a. Circuit controlling lamp damaged.
Code: 56 “32 Pin” (MSE 1.1) Plastic-
Cased ECU only.
Source: Fuel pump relay circuit open, shorted
to ground, or shorted to battery.
Explanation: Fuel pump, ignition coils, and fuel
injectors will not function because the
fuel pump relay circuit is either open,
shorted to ground, or may be “on”
continuously if shorted to battery.
Expected Engine
Response: Engine will not run, or fuel pump will
continue to run when switch is off.
Possible Causes:
1. Fuel Pump Relay Related
a. Bad fuel pump relay.
Primary side open or shorted.
2. Fuel Pump Related
a. Fuel pump open or shorted internally.
3. Engine Wiring Harness related
a. Fuel pump fuse F1 open.
b. Broken or shorted wire in harness.
ECU pin 28 to fuel pump relay pin 86.
Ignition switch to fuel pump relay pin 85.
4. ECU Related
a. Circuit controlling fuel pump relay damaged.