G3306B Petroleum Generator Set Engines Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the speed/timing sensor. Also use this procedure if the diagnostic code in Table 1 is active or easily repeated.

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

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

Table 2

Troubleshooting Test Steps	Values	Results
1. Perform a Visual Inspection of the Installation of the Speed/Timing Sensor and Connector A. Remove the electrical power from the ECM. B. Visually inspect the installation of the sensor. Do not remove the sensor from the front housing. C. Visually inspect the condition of the sensor and connector. Check that the components are not cracked or broken. D. Check that the mounting bolt is tight and that hold-down bracket (4) is not bent or deformed. E. Ensure that the sensor mounting flange (3) is flush against the housing. Check that the sensor is not loose in the housing bore. F. Remove the harness connector from the sensor and visually inspect the connection at the sensor. G. Check the inside of the harness connector for debris, moisture, and/or corrosion. H. Perform a 45 N (10 lb) pull test on each of the wires at the harness connector. I. Check the sensor connector seal for damage. Ensure that the harness connector securely locks onto the sensor. J. Visually inspect the harness around the sensor connector for damage. Ensure that the harness has not been damaged by rubbing on rotating components.	Damaged connector, wiring, or sensor	Result: The sensor is installed correctly and the harness connector is in good repair. Proceed to Test Step 2. Result: A problem has been found with the installation of the sensor and/or harness or the harness connector. 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.

Illustration 6	g01993813
Test lead connections at the multimeter for the current measurement at the harness connector (typical multimeter)

Table 3

Troubleshooting Test Steps	Values	Results
2. Use a Multimeter to Check the Condition of the Harness A. Ensure that the electrical power has been removed from the ECM. Ensure that the harness connector is disconnected at the sensor. B.Connect Caterpillar Electronic Technician (ET) to the service tool connector. C. Restore the electrical power to the ECM. D. 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. E. Monitor the active diagnostic code and the logged diagnostic codes on Cat ET. Check for an active 678-4ECU 8 Volts DC Supply : Voltage Below Normal. For a signal wire that is in good repair, a 678-4 diagnostic code will not be active while the multimeter is installed in the circuit. F. Use the multimeter to measure the DC amperage of the circuit. If the signal wire is shorted to engine ground, an attempt to measure the amperage in the circuit will short out the power supply. As the amperage exceeds the design of the power supply, the ECM will momentarily switch off the power for the circuit. Then, the ECM will again attempt to power the circuit and the cycle will continue. Be sure to check for an active diagnostic code for the power supply if you suspect that this condition exists.	Harness condition	Result: The 678-4 diagnostic code is not active and the DC amperage is greater than 10 mA. The harness wiring appears to be OK. Proceed to Test Step 3. Result: A 678-4 diagnostic code becomes active when the ammeter is placed in the circuit. There is a short to ground in the signal wire between the ECM and the sensor harness connector. Repair the signal wire or replace the signal wire. Ensure that the locking tab for the sensor connector is securely locked and ensure that the wire tie at the sensor is securely in place. Validate the repair by rechecking the DC amperage for the circuit. If the amperage of the circuit is OK after the repair, check for an active 190-8 diagnostic code. If the code is not active, start the engine and clear the logged codes that are related to this problem. If the repair has resolved the original problem, return the engine to service. Result: The DC amperage is less than 10 mA in the circuit. There is an open circuit in the supply wire or the signal wire that is in the engine harness. Perform the following procedure: 1. Ensure that the electrical power to the ECM has been restored. 2. At the harness connector for the sensor, use a multimeter to check for a supply voltage between terminal 1 and engine ground. If 8.0 ± 0.4 VDC is measured between terminal 1 and engine ground at the harness connector for the sensor, the supply circuit is OK. There is an open circuit in the signal wire between the ECM and the sensor. Repair the harness or replace the harness. Ensure that the locking tab for the sensor connector is securely locked and ensure that the wire tie at the sensor is securely in place. If the voltage between terminal 1 and engine ground is less than 7.0 VDC, there is an open circuit in the supply circuit. Repair the harness or replace the harness. Ensure that the locking tab for the sensor connector is securely locked and ensure that the wire tie at the sensor is securely in place. Validate the repair by rechecking the DC amperage for the circuit. If the amperage of the circuit is OK after the repair, check for an active 190-8 diagnostic code. If the code is not active, start the engine and clear the logged codes that are related to this problem. If the repair has resolved the original problem, return the engine to service.

Table 4

Troubleshooting Test Steps	Values	Results
3. Check the Sensor for Visible Damage to the Pickup Head A. Ensure that the electrical power is removed from the ECM. B. Remove the speed/timing sensor from the front housing of the engine. C. Inspect the sensor pickup head for damage that is caused by scraping the timing ring.	Damaged sensor	Result: There is no visible damage to the speed/timing sensor. The problem may be damage to the internal circuitry of the speed/timing sensor. Install a new speed/timing sensor on the engine. Ensure that the locking tab for the sensor connector is securely locked and ensure that the wire tie at the sensor is securely in place. Validate the repair by performing the following procedure: 1. Attempt to start the engine. Use Cat ET to check for an active 190-8 diagnostic code. 2. If the engine starts and the code is not active, clear the logged codes that are related to this problem. Return the engine to service. 3. If the code remains active, there is probably an intermittent problem in the harness or in a connector. Perform this procedure again in order to locate the problem and make the necessary repairs. Result: The sensor has been damaged from contact with the timing ring. There appears to be a mechanical problem in the front gear train. Check the front gear train for components that have become loose or damaged. Perform the necessary repairs. Replace the damaged sensor. Ensure that the locking tab for the sensor connector is securely locked and ensure that the wire tie at the sensor is securely in place. Validate the repair by performing the following procedure: Attempt to start the engine. Use the electronic service tool to check for an active 190-8 diagnostic code. If the engine starts and the code is not active, clear the logged codes that are related to this problem. Return the engine to service.