Exhaust Back Pressure Regulator (EPR)

1996 PCED OBDI

SECTION 18: Diesel Diagnosis — 7.3L DI Engine

M: Exhaust Back Pressure Regulator (EPR)
Introduction

Output Functions

Exhaust Back Pressure Regulator (EPR) — 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 powertrain control module (PCM) uses the measured exhaust back pressure, intake air temperature and engine load to determine the desired exhaust back 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 exhaust back pressure (EBP) or intake air temperature (IAT) sensor fault it will disable the exhaust back pressure device.

Note

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

HARNESS CONNECTOR CHECKS TO GROUND (B-)
(CHECK WITH REGULATOR CONNECTOR DISCONNECTED)
Test Points	Spec.	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.

HARNESS EPR VOLTAGE CHECK
(CHECK WITH REGULATOR AND EOT SENSOR CONNECTOR DISCONNECTED)
Test Points	Spec.	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 engine oil temperature (EOT) sensor causes -40°F default to be set forcing the EPR on. A code 0198 (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

0475 = Exhaust pressure control valve malfunction.

0476 = Exhaust pressure control valve performance.

M: Pinpoint Tests