Exhaust Back Pressure (EPR) Regulator

Output Functions

Exhaust Back Pressure Regulator

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) intake air temperature, engine oil 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 modulated from 0 to 99% dependent upon the exhaust back pressure desired.

Upon each initial engine start-up, the PCM exercises the exhaust back pressure valve by commanding it to cycle on and off once. If upon start-up the temperature of intake air sensed by the IAT sensor is < 37°F (5°C) and the oil temperature sensed by the EOT sensor is between 32°-140°F (0-60°C) it will continue to keep the back pressure valve partially closed. As the oil temperature rises during engine operation, the PCM will control the valve in response to the rising oil temperature.

Fault Detection/Management

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

Problems with either the Exhaust Back Pressure Device or the tube between the exhaust manifold and the EBP sensor can be detected during the exhaust back pressure step test, in which the PCM commands and then measures a specific preprogrammed pressure and then measures time for pressure decay during the engine running test.

If the PCM detects and EBP, EOT or IAT sensor fault it will disable the exhaust back pressure regulator.

NOTE: After removing connector always check for damaged pins, corrosion, loose terminals etc.

Connector Checks to Ground (B-) (Check with Sensor Connector Disconnected and Ignition key off, all accessories off)

Test Points	Spec	Comments
A to Grd.	< 5 ohms	Resistance greater than 5 ohms indicates an open circuit or bad ground
B to Grd.	> 1000 ohms	Resistance less than 1000 ohms indicates a short to ground

Harness Resistance Checks (Check with breakout box installed on engine harness only)

Test Points	Spec	Comments
Pwr. Grd. to Pin #42	2.5 to 20 ohms	Resistance through EPR circuit including regulator, check with regulator connector connected (unnecessary to check next points if okay)
A to Grd.	< 5 ohms	Resistance from regulator connector to Pwr. Ground
B to #42	< 5 ohms	Resistance from regulator connector to 104 pin connector

Circuit Fault Code Descriptions
0475 = Output circuit check detected during Standard test, indicates high or low resistance in circuit
Exhaust Back Pressure System Fault Code Descriptions
0478 = EPR pressure was greater than 71 in.Hg., (340 kpaG), (35 PSI) for 2.5 seconds.
0476 = Indicates that EPR pressure of 22 in.Hg. (75 kPa) commanded during EBP engine running test was not obtained (Plugged line or exhaust back pressure device failure.)