Exhaust Back Pressure (EPR) Regulator

1994 PCED OBDI-A

SECTION 18A: Diesel Diagnosis — 7.3L DI Engine

M: Exhaust Back Pressure (EPR) Regulator
Introduction

Output Functions

Exhaust Back Pressure Regulator — Is a variable position valve that controls exhaust back pressure during cold ambient temperatures to increase cab heat and decrease the amount of time needed to defrost the windshield. The PCM uses the measured exhaust back pressure, ambient air temperature and engine load to determine the desired exhaust back pressure injection control pressure.

Valve position is controlled by switching the output signal circuit to 12 volts inside the PCM. On/off time is dependent upon the exhaust back pressure.

Detection/Management

An open or shorted to ground control circuit can be detected by an on demand output circuit check performed during the KOEO test.

An exhaust back pressure step test, in which the PCM commands and then measures specific preprogrammed pressures, is performed during the KOER test.

If the PCM detects an EBP or IAT sensor fault it will disable the exhaust back pressure device.

Note

After removing connectors always check for damaged pins, corrosion, loose terminals, etc.

Connector Checks to Ground (B-)
(Check with regulator connector disconnected)
Test Points	Spec.	Actual	Comments
A to Grd	<5 ohms		Resistance greater than 5 ohms indicates an open circuit.
B to Grd	>5 ohms		Resistance less than 5 ohms indicates a short to ground.

EPR Voltage Check
(Check with regulator and EOT sensor connector disconnected)
Test Points	Spec.	Actual	Comments
A to Grd	0-.25 volts		If greater than .25 volts signal wire is shorted to VREF or battery.
B to Grd	12 volts		Control voltage from the PCM, unplugging the EOT sensor causes -40°F default to be set forcing the EPR on. A code 118 (EOT high) will also be set.

Harness Resistance Checks
(Check with breakout box installed on harness only)
Test Points	Spec.	Comments
No. 42 to Pwr. Grd	2.5 to 12 ohms	Resistance through EPR circuit including regulator; check with regulator connector connected.
No. 42 to B	<5 ohms	Resistance from regulator connector to 104 pin connector.
A to Pwr. Grd	<5 ohms	Resistance from regulator connector to power ground.

DTC Descriptions

514 = Output circuit check detected during KOEO test indicates high or low resistance in circuit.

842 = EBP signal or pressure not responding during KOER On-Demand Test (refer to Supplemental Diagnostics — EBP control tests).

M: Pinpoint Tests