Circuit DescriptionThe intake manifold air temperature sensor is used by the engine control module (ECM) tomonitor the engine intake air temperature. The intake manifold air temperature signal is used by the ECM for engine protection system, cold start aid, timing, and fueling control. Component LocationThe intake manifold air temperature sensor is located on the side of the intake manifold at the rear of the head. Cummins ISB CM550 (1990-94) Fault Code: 154 PID: 105 SPN: 105 FMI: 3 Intake Manifold Air Temperature Sensor Circuit Cummins ISB CM550 (1990-94) Fault Code: 153 PID: 105 SPN: 105 FMI: 4 Intake Manifold Air...

Circuit DescriptionThe intake manifold air temperature sensor is used by the electronic control module (ECM) to monitor the temperature of the engine intake air. The intake air temperature is used by the ECM for the engine protection system, cold start aids, and the timing and fueling control. Component LocationThe intake manifold temperature sensor is located on the side of the intake manifold toward the rear of the cylinder head. Shop Talk1) Make sure the engine compartment temperature does not get too high (above 93.3°C[200°F]).2) Make sure the intake manifold temperature sensor is not located near any extreme heatsources. Possible causes:1)...

Circuit DescriptionThe air conditioner clutch solenoid is a device used by the electronic control module (ECM) to control the air conditioner by sending a signal to open or close the air conditioner clutch solenoid. Component LocationRefer to an original equipment manufacturer’s (OEM) diagram for the location of the air conditionerclutch solenoid. Shop TalkAir conditioner clutch solenoid could be malfunctioning due to a failed engine harness or a bad ground on the air conditioner clutch connector. Cummins ISB CM550 (1990-94) Fault Code: 155 PID: 105 SPN: 105 FMI: 0 Intake Manifold Air Temperature Sensor – Engine Protection Circuit Cummins ISB CM550...

Circuit DescriptionThe ambient air pressure sensor monitors atmospheric pressure and passes information to the electronic control module (ECM) through the sensor harness. Component LocationThe ambient air pressure sensor is located below the fuel transfer pump. Shop TalkMonitor the ambient air pressure reading with a service tool to confirm that the pressure reading matches the actual air pressure. The ambient air pressure sensor is required with 300 horsepower rated engines and specific 275 horsepower rated engines. Cummins ISB CM550 (1990-94) Fault Code: 191 PID: 50 SPN: 876 FMI: 11 Air Conditioner Clutch Supply Circuit Cummins ISB CM550 (1990-94) Fault Code: 155...

Circuit DescriptionThe ambient air pressure sensor monitors atmospheric pressure and passes information to the electronic control module (ECM) through the sensor harness. Component LocationThe ambient air pressure sensor is located below the fuel transfer pump. Shop TalkMonitor the ambient air pressure reading with a service tool to confirm that the pressure reading matches the actual air pressure. The ambient air pressure sensor is required with 300 horsepower rated engines and specific 275 horsepower rated engines. Cummins ISB CM550 (1990-94) Fault Code: 221 PID: 108 SPN: 108 FMI: 3 Ambient Air Pressue Sensor Circuit Cummins ISB CM550 (1990-94) Fault Code: 191...