Circuit DescriptionThe engine speed sensor provides engine speed information to the electronic control module (ECM). The sensor must be powered up by +5 VDC to operate.The sensor generates its signals by sensing the movement of target teeth cast into a tone wheel that is mounted to the crankshaft. The tone wheel has 35 teeth and a gap where the 36th tooth would be placed. This missing tooth indicates that cylinder No. 1 (and No. 6) is at top dead center. Component LocationThe engine speed sensor is located on the intake side of the engine block, at crankshaft level, between cylinders...

Circuit DescriptionThe coolant level sensor monitors the coolant level within the coolant system and passesinformation to the electronic control module (ECM) through the engine harness. Because this sensor is so complex, do not use a multimeter to check it. If the radiator coolant level drops below a certain level, a progressive power and/or speed derate will occur. Engine can,perhaps, shut down if engine protection shutdown feature is enabled. Component LocationThe coolant level sensor is located in the radiator top tank or surge tank. Shop TalkThis is an OEM supplied component and can vary in location.1) If a shorting plug is...

Circuit DescriptionThe vehicle speed sensor (VSS) uses two separate coils of wire (some applications use asingle-coil sensor) to count gear teeth as they pass in front of the sensor. One coil is used bythe electronic control module (ECM) to sense vehicle speed. The other coil is sometimes used by the OEM to send a vehicle speed signal to the speedometer. Component LocationThe VSS is most commonly installed in the rear of the transmission. Shop Talk1) Disconnect the vehicle speed sensor connector that connects to the OEM speedometer,or trip recorder, and move the truck. If the fault goes inactive, there is...

Circuit DescriptionThe vehicle speed sensor (VSS) uses two separate coils of wire (some applications use asingle-coil sensor) to count gear teeth as they pass in front of the sensor. One coil is used bythe electronic control module (ECM) to sense vehicle speed. The other coil is sometimes used by the OEM to send a vehicle speed signal to the speedometer. Component LocationThe VSS is most commonly installed in the rear of the transmission. Shop Talk1) Verify that the feature settings for VSS antitampering (Fault Code 242), application typeand automatic transmission are set correctly. If any of these are set incorrectly,...

Circuit DescriptionThe electronic control module (ECM) enables the exhaust brake by sending a signal to therelay that controls the exhaust brake under certain conditions. Component LocationRefer to the original equipment manufacturer’s (OEM) diagram for the location of the engine brake. Cummins ISB CM550 (1990-94) Fault Code: 242 PID: 84 SPN: 84 FMI: 10 Vehicle Speed Sensor (VSS Circuit Cummins ISB CM550 (1990-94) Fault Code: 241 PID: 84 SPN: 84 FMI: 2 Vehicle Speed Sensor Circuit Cummins ISB CM550 (1990-94) Fault Code: 235 PID: 111 SPN: 111 FMI: 1 Engine Coolant Level – Engine Protection Cummins ISB CM550 (1990-94) Fault Code:...