Diagnostic Aids
The injector control pressure is determined by the Injection Pressure Regulator (IPR). The IPR is a variable position valve that controls injection control pressure. The PCM uses many input variables to determine the desired control pressure. Battery voltage is supplied to the IPR when the ignition is in the ON position. Valve position is controlled by switching the output signal circuit to ground. The ON/OFF time is modulated from 0-50 percent dependent upon the desired control pressure.
The ICP sensor bias varies between sensors. The amount of voltage the sensor deviates from a calculated reference value (sensor bias) may cause an injection control pressure calculation error.
An open or shorted to ground control circuit can be detected by an on demand output circuit check performed during the KOEO test. When the starter is engaged and the engine fails to start, the IPR command will increase toward its maximum until the engine starts. The normal range for the IPR at idle is between 8-16 percent. An above 16 percent range indicates high effort to achieve idle. A below 8 percent indicates low effort to achieve idle. The PCM is capable of detecting whether desired injection control pressure is equal to the measured injection control pressure while the engine is running. If the measured injection control pressure does not reasonably compare to the desired injection control pressure the PCM ignores the measured ICP sensor signal and attempts to control the engine with the desired value. (If the problem was in the sensor circuit, this strategy causes little performance deterioration. If the problem is in the control circuit, engine performance will probably still be unsatisfactory). An injection control pressure step test, in which the PCM commands and then measures calibrated pressures, is performed during the KOER test.