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Table 1
Diagnostic Codes Table
Description Conditions which Generate this Code System Response
190-8 Engine Speed: Abnormal Frequency, Pulse Width or Period The Electronic Control Module (ECM) detects an intermittent loss or complete loss of the signal from the speed/timing sensor.
The engine control switch has been in the RUN position for at least 3 seconds. The code is logged.
The red stop lamp is illuminated.
The engine is shut down.
678-3 ECU 8 Volts DC Supply : Voltage Above Normal The 8 v sensor supply voltage has risen above 8.8 v for 1.5 seconds.
The engine control switch has been in the RUN position for at least 3 seconds. The 190-8 diagnostic code is suppressed while this code is active.
The code is logged.
The amber warning lamp is illuminated.
The service tool displays "Error Indicator" on the status screen for this parameter.
678-4 ECU 8 Volts DC Supply : Voltage Below Normal The 8 v sensor supply voltage has dropped below 7.2 v for 1.5 seconds.
The engine control switch has been in the RUN position for at least 3 seconds. The 190-8 diagnostic code is suppressed while this code is active.
The code is logged.
The amber warning lamp is illuminated.
The service tool displays "Error Indicator" on the status screen for this parameter. The speed/timing sensor provides information about engine speed and the position of the camshaft to the engine ECM. A timing ring is mounted to the front of the camshaft gear. The sensor is mounted above the timing ring. As the teeth of the timing ring rotate past the pickup head, a signal is generated. The signal matches the pattern of the teeth that are on the timing ring. This signal is detected by the ECM.With the information from the speed/timing sensor, the ECM is able to calculate the position of the pistons in the cylinders. The ECM determines the desired ignition timing according to the engine speed and load. The ECM sends voltage pulses to the ignition transformers for firing the spark plugs according to the desired timing.Note: The speed/timing sensor is an active sensor that utilizes an 8 v supply voltage and integrated circuitry. Do not attempt to troubleshoot the sensor by measuring resistance across the terminals of the sensor.If a problem is detected with the signal from the speed/timing sensor during engine operation, the ECM will shut down the engine. The ECM activates the above diagnostic code.The least likely cause of this diagnostic code is a problem with the ECM.
Illustration 1 g01918293
Schematic for the engine speed/timing sensor
Illustration 2 g01918294
Location of the speed/timing sensor (right front side engine view)
(1) P2 ECM connector
(2) Speed/timing sensor
Illustration 3 g01918833
Terminal locations at the P2 ECM connector
(10) +8 v sensor supply
(52) Engine speed/timing signal
Illustration 4 g01919073
Terminal locations at the speed/timing sensor
(1) +8 v sensor supply
(2) Engine speed/timing signal Test Step 1. Perform a Visual Inspection of the Installation of the Speed/Timing Sensor and Connector
Remove the electrical power from the ECM.
Illustration 5 g01987313
Speed/timing sensor (typical right front engine view)
(3) Sensor mounting flange
(4) Hold-down bracket
(5) Wire tie at the sensor
Visually inspect the installation of the sensor. Do not remove the sensor from the front housing.
Visually inspect the condition of the sensor and connector. Check that the components are not cracked or broken.
Check that the mounting bolt is tight and that hold-down bracket (4) is not bent or deformed.
Ensure that the sensor mounting flange (3) is flush against the housing. Check that the sensor is not loose in the housing bore.
Remove the harness connector from the sensor and visually inspect the connection at the sensor.
Check the inside of the harness connector for debris, moisture, and/or corrosion.
Perform a 45 N (10 lb) pull test on each of the wires at the harness connector.
Check the sensor connector seal for damage. Ensure that the harness connector securely locks onto the sensor.
Visually inspect the harness around the sensor connector for damage. Ensure that the harness has not been damaged by rubbing on rotating components. Expected Result:The inspection confirmed that the installation of the sensor and the condition of the harness and connector are OK.Results:
OK - The sensor is installed correctly and the harness connector is in good repair. Proceed to Test Step 2.
Not OK - A problem has been found with the installation of the sensor and/or harness or the harness connector.Repair: Perform the necessary repairs. Correct any adverse conditions that have been identified by the inspection. Replace any damaged components. Ensure that the wire tie (5) at the sensor is securely in place.Attempt to start the engine. If the repair eliminates the original problem, return the engine into service. If the problem persists, continue to the next Test Step.STOPTest Step 2. Use a Multimeter to Check the Condition of the Harness
Ensure that the electrical power has been removed from the ECM. Ensure that the harness connector is disconnected at the sensor.
Connect Caterpillar Electronic Technician (ET) to the service tool connector.
Restore the electrical power to the ECM.
Illustration 6 g01993813
Test lead connections at the multimeter for the current measurement at the harness connector (typical multimeter)
Connect the test leads to the connections on the multimeter that are for measuring milliamperes ("mAµA"). Install the other end of the leads between socket terminals 1 and 2 on the harness side of the sensor connector. Place the multimeter on the "mA" scale.
Monitor the active diagnostic code and the logged diagnostic codes on Cat ET. Check for an active 678-4 ECU 8 Volts DC Supply : Voltage Below Normal.