SIGNAL 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) 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 an EBP, EOT or IAT sensor fault it will disable
the exhaust back pressure regulator.
After removing connector always check for
damaged pins, corrosion, loose terminals, etc.
| Connector Checks to Ground (B-) |
| (Check with Regulator Connector Disconnected, Ignition key off, all accessories off.) |
| Test Points |
Spec. |
Comments |
| A to Grd. |
< 5 ohms |
Resistance greater then 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. Gnd. to Pin #42 |
2.5 to 20 ohms |
Resistance through EPR circuit including regulator, check
w/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.) |
|
