We have found problem with this unit, a piece of wax from propane system got stuck under air/fuel mixer diaphragm, complete assy was changed by first service company. Even though EPR and vapor line was cleaned by us.

there should be fuses on the engine cover where a diagnostic port is

CAUSE D - CAN LO SHORTED TO UNSWITCHED OR SWITCHED BATT +
PROCEDURE OR ACTION:
1. Ensure truck power is OFF.
2. Ensure disconnection of EPR, ECM, and engine to main harness connector that carries the CAN circuit.
3. Change DMM to volts scale.
4. At the EPR connector, measure voltage between the Can Lo circuit and a clean vehicle ground.
Is voltage approximately system voltage?
YES: CAN Lo wire is shorted to a unswitched battery circuit. Locate and repair/replace open wire/connection.
See Wire Harness Repair 2200SRM1128.
NO: Go to Step 5.
5. Turn truck power ON.
6. Repeat Step 4.
Is voltage approximately system voltage?
YES: CAN Lo wire is shorted to a switched battery circuit. Locate and repair/replace open wire/connection.
See Wire Harness Repair 2200SRM1128.
NO: Go to Cause E.
CAUSE E - EPR FAILURE
PROCEDURE OR ACTION:
1. Ensure truck power is OFF.
2. Replace EPR. See LPG Fuel System 0900SRM1125 and Wire Harness Repair 2200SRM1128. For GM
5.7L LPG and GM 4.3L LPG engines with PSI, see LPG Fuel System 0900SRM1433 or LPG Fuel System,
GM 4.3L Engine With PSI 0900SRM1556.
3. Repeat Component Operational Check.
Does DTC reoccur?
YES: Repeat Cause A through Cause D
NO: Problem is corrected. Resume operation.
END POSSIBLE CAUSES

CAUSE C - CAN HI SHORTED TO GROUND
PROCEDURE OR ACTION:
1. Ensure truck power is OFF.
2. Ensure disconnection of EPR, ECM, and engine to main harness connector that carries the CAN circuit.
3. Change DMM to ohms scale. Verify DMM zero reading.
4. At the EPR connector, measure resistance between the Can Hi circuit and a clean vehicle ground.
Is resistance less than 0.5 ohms?
YES: CAN Hi wire is shorted to a ground circuit. Locate and repair/replace open wire/connection. See Wire
Harness Repair 2200SRM1128.
NO: Go to Cause D.
Diagnostic Trouble Codes Electrical System
Check the Service Manual section in Hypass Online for possible updates and check pertinent Grams
9030-20-

CAUSE B - CAN HI OR CAN LO OPEN CIRCUIT
PROCEDURE OR ACTION:
1. Ensure truck power is OFF.
2. Disconnect EPR, ECM, and engine to main harness connector that carries the CAN circuit.
3. Change DMM to ohms scale. Verify DMM zero reading.
4. Ensure connector pins are fully seated in their respective housing.
5. At the EPR connector and ECM connector, measure resistance between the two pins on the Can Hi circuit.
Is resistance less than 0.5 ohms?
YES: Go to Step 6.
NO: CAN Hi wire is open circuit. Locate and repair/replace open wire/connection. See Wire Harness Repair
2200SRM1128.
6. At the EPR connector and ECM connector, measure resistance between the two pins on the Can Lo circuit.
Is resistance less than 0.5 ohms?
YES: Go to Cause C.
NO: CAN Lo wire is open circuit. Locate and repair/replace open wire/connection. See Wire Harness Repair
2200SRM1128.

COMPONENT OPERATIONAL CHECK
PROCEDURE OR ACTION:
1. Turn power to OFF for no less than 30 seconds, and then to ON to clear displayed DTC.
Does reported DTC reoccur?
YES: Go to Step 2.
NO: Problem not verified. Resume operation.
2. Conduct a quick visual inspection of all connectors/wiring associated with the displayed fault code.
Are any faults detected/observed?
YES: Repair/replace connector or wiring associated with faults found. See Electrical System 2200SRM1142.
NO: Go to Cause A.
CAUSE A - EPR SUPPLY/GROUND OPEN CIRCUIT
PROCEDURE OR ACTION:
1. Change DMM to ohms scale. Verify DMM zero reading.
2. Turn truck power ON.
3. At EPR harness connector, measure voltage between EPR supply pin (+) and EPR battery (-) ground.
Is voltage approximately system voltage?
YES: Go to Cause B.
NO: Go to Step 4.
4. At 10 Amp EPR fuse, measure voltage between both sides of the fuse and EPR connector ground.
Is voltage approximately equal to Batt Vdc on both sides of the fuse?
YES: EPR supply circuit or ground circuit is open between EPR connector and the EPR fuse/main engine
ground. Locate and repair/replace open wire/connection. See Wire Harness Repair 2200SRM1128.
NO: Go to Step 5.
5. Inspect harness between fuse and EPR connection for a short to ground/frame. Locate and repair/replace
shorted wire/connection. See Wire Harness Repair 2200SRM1128.
6. Replace fuse with correct current rated part.
7. Repeat Cause AStep 2
Is voltage approximately system voltage?
YES: Go to Cause B.
NO: Go to Step 8.
8. Refer to power distribution module mini-schematic and check all switched battery circuits for open circuits/
shorts to vehicle ground/frame. Follow procedures as outlined in DTC 522762-4. Locate and repair/replace
shorted wire/connection. See Wire Harness Repair 2200SRM1128