G3516C, G3516E, and G3512E Generator Set Engines Caterpillar

Illustration 1	g01089416
Speed/Timing sensor and timing ring

Use this procedure to troubleshoot suspect problems with the circuit for the speed/timing sensor.

This procedure covers the following diagnostic codes:

• 320-3 Speed/Timing Sensor short to +batt

• 320-7 Speed/Timing Sensor improper response

• 320-8 Engine Speed/Timing signal abnormal

The speed/timing sensor provides information about engine speed and the position of the crankshaft to the Electronic Control Module (ECM). The sensor is powered by the sensor supply (12 VDC) from the ECM. A magnetic pickup is located underneath the plastic sliphead of the sensor. The timing ring is mounted on the rear of the left camshaft. As the teeth of the ring rotate past the sliphead of the sensor, the sensor generates a signal that matches the pattern of the teeth.

The timing ring has a special tooth pattern that indicates the position of the camshaft and the direction of rotation. The timing ring has 24 slots in the outer diameter. 21 of the slots are narrow. Three of the slots are about 2.5 times wider than the rest of the slots. When the engine rotates in the normal direction, the slots pass the speed/timing sensor in the following order:

• 1 wide slot

• 3 narrow slots

• 2 wide slots

• 18 narrow slots

The number one cylinder is at the top center position when the rising edge of the third narrow slot passes the center of the sliphead. All 24 teeth pass the sliphead during one revolution of the camshaft or two revolutions of the crankshaft.

With the information from the engine speed/timing sensor, the ECM is able to calculate the positions of the pistons in the cylinders. The ECM determines the desired ignition timing according to the engine speed and load. If detonation is detected in any of the cylinders, the appropriate ECM retards the timing of the affected cylinders. The ECM sends voltage pulses to the ignition transformers for firing the spark plugs according to the desired timing.

During engine operation, the ECM will shut down the engine if the ECM detects a problem with the signal from the speed/timing sensor. The ECM will activate the corresponding diagnostic code.

If there is a problem with the engine speed/timing sensor's signal during start-up but no corresponding diagnostic code is active, the ECM will not initiate the ignition. The engine will not start. The corresponding diagnostic code is not activated.

The most likely causes of the diagnostic code are a poor electrical connection or a problem in a wiring harness. The next likely cause is a problem with the engine speed/timing sensor. The least likely cause is a problem with the ECM.

Logged diagnostic codes provide a historical record. Before you begin this procedure, use Caterpillar Electronic Technician (ET) to print the logged codes to a file.

The troubleshooting procedure may generate additional diagnostic codes. Keep your mind on correcting the cause of the original diagnostic code. Clear the diagnostic codes after the problem is resolved.

Illustration 2	g01325649
Schematic for the circuit of the speed/timing sensor

Test Step 1. Inspect the Electrical Connectors and Wiring

1. Remove the electrical power from the engine.

   Note: For the following steps, refer to Troubleshooting, "Electrical Connectors - Inspect".

2. Thoroughly inspect the following connections:

   • J1/P1 connectors

   • J7/P7 connectors

   1. Check the torque of the allen head screw for the ECM connectors.
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      Illustration 3	g01055533
      Harness side of the ECM P1 connector (P1-33) Signal (P1-43) 12 volt supply (P1-51) Return

   2. Perform a 45 N (10 lb) pull test on the wires that are associated with the circuit for the speed/timing sensor.
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      Illustration 4	g01525136
      Left side view (1) Speed/timing sensor

   3. Check the harness and wiring for abrasion and for pinch points from the speed/timing sensor to the ECM.

Expected Result:

The connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points.

Results:

• OK - The components are in good condition with proper connections. Proceed to Test Step 2.

• Not OK - The components are not in good condition and/or at least one connection is improper.

  Repair: Perform the necessary repairs and/or replace parts, if necessary.

  STOP

Test Step 2. Check the Sensor

1. Set the engine control to the OFF/RESET mode. Switch the 35 amp circuit breaker OFF.

2. Remove the speed/timing sensor.
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   Illustration 5	g00931748
   Plastic sliphead for the speed/timing sensor

3. Inspect the condition of the plastic sliphead. Look for signs of wear and for contaminants. Clean any debris from the plastic sliphead.

4. Check the tension of the plastic sliphead. Gently extend the plastic sliphead for a minimum of 4 mm (0.16 inch). Then push back the plastic sliphead.

Expected Result:

The sensor is in good condition. At least 22 N (5 lb) of force is required to push in the plastic sliphead from the extended position.

Results:

• OK - The sensor is not damaged. The tension of the plastic sliphead is correct.

  Repair: Install the sensor.

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  NOTICE
  The plastic sliphead must be fully extended when the speed/timing sensor is installed so that the sensor maintains the correct clearance with the timing ring. If the correct clearance is not maintained, the signal from the sensor will not be generated. Do not install the sensor's plastic sliphead between the teeth of the timing ring. Damage to the plasic sliphead will result. Before installing the sensor, ensure that a tooth of the ring is visible in the mounting hole for the sensor.

  1. Use the following steps to install the speed/timing sensor:

     1. Ensure that a tooth on the timing ring is visible in the mounting hole for the sensor.

     2. Fully extend the sliphead.

        Note: The plastic sliphead is designed to contact the tooth of the timing ring during installation. As the timing ring begins to turn, the radial runout of the timing ring will push the plastic sliphead into the sensor body slightly. This provides the plastic sliphead's air gap with a self-adjusting function. The maximum allowable clearance between the sliphead and a tooth on the timing ring is 0.5 mm (0.02 inch).

     3. Coat the threads of the sensor with 4C-5597 Anti-Seize Compound.

     4. Install the sensor. Tighten the sensor to 40 ± 5 N·m (30 ± 4 lb ft).

  Proceed to Test Step 3.

• Not OK - The plastic sliphead is damaged and/or the tension of the sliphead is insufficient.

  Repair: Install a new sensor. Calibrate the sensor. Refer to Troubleshooting, "Timing - Calibrate".

  If the condition is not resolved, proceed to Test Step 3.

Test Step 3. Check for Active Diagnostic Codes for the 12 Volt Sensor Supply

1. Connect Cat ET to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

2. Switch the 35 amp circuit breaker ON. Set the engine control to the STOP mode.

3. Use the "Active Diagnostic" screen on Cat ET. Look for the following codes:

   • 145-3 12 Volt DC Power Supply : Voltage Above Normal

   • 145-4 12 Volt DC Power Supply : Voltage Below Normal

Expected Result:

None of the above codes are active.

Results:

• No active codes - None of the above codes are active. However, at least one of the codes is logged.

  Repair: Clear the logged codes.

  Proceed to Test Step 4.

• Active code - One of the above codes is active. Proceed to Test Step 5.

Test Step 4. Use Cat ET to Check the Engine RPM

1. Use the "Status - Group 1" screen in order to observe "Engine Speed". Observe the "Engine Speed" parameter on the screen and set the engine control to the START mode. Crank the engine.

2. Continue to observe the screen and allow the engine rpm to stabilize at the normal cranking speed.

3. Set the engine control to the STOP mode.

Expected Result:

Before the engine is cranked, the engine speed is "0". The engine speed increases until the speed stabilizes at the normal cranking speed. When the engine is stopped, the speed decreases back to "0". A diagnostic code for the speed/timing sensor is not active.

Results:

• OK - The engine started and the engine ran properly. A diagnostic code for the speed/timing sensor was not activated. The speed/timing sensor is operating properly.

  STOP

• Not OK - The engine cranked. However, Cat ET did not display the correct engine speed or a diagnostic code for the speed/timing sensor was activated. Proceed to Test Step 5.

• Not OK - The engine cranked but the engine did not start. Cat ET displayed the correct engine speed. A diagnostic code for the speed/timing sensor was not activated. The ECM is receiving a valid signal.

  Repair: Refer to Troubleshooting, "Engine Cranks but Does Not Start". Make repairs, as needed.

  STOP

Test Step 5. Measure the Sensor Supply Voltage at the Sensor

1. Set the engine control to the OFF mode.

2. Install a 8T-8726 Adapter Cable As (3-PIN BREAKOUT) in series with the connectors for the speed/timing sensor.

3. Set the engine control to the STOP mode. Measure the supply voltage between terminals "A" and "B" of the breakout t.

Expected Result:

The voltage is between 11.5 VDC and 13.5 VDC. A 145-3 diagnostic code or a 145-4 diagnostic code is not active.

Results:

• OK - The sensor is receiving correct supply voltage. A 145-3 diagnostic code or a 145-4 diagnostic code is not active. Leave the breakout t connected. Proceed to Test Step 6.

• Not OK - The sensor is not receiving correct supply voltage or a 145-3 diagnostic code or a 145-4 diagnostic code is active. Remove the breakout t. Proceed to Test Step 7.

Test Step 6. Isolate the Signal Voltage at the Sensor

1. Set the engine control to the OFF/RESET mode.

2. Ensure that the breakout t is connected in series with the connectors for the speed/timing sensor.

3. Remove the wire from terminal "C" of the breakout t in order to isolate the sensor signal wire.

4. Set the engine control to the STOP mode. Measure the signal voltage between terminals "B" and "C".

5. Set the engine control to the START mode. Crank the engine and measure the signal voltage between terminals "B" and "C".

Expected Result:

When the engine control is in the STOP mode, the voltage is less than 3.0 VDC or the voltage is greater than 10.0 VDC.

The voltage varied between 2.0 VDC and 4.0 VDC during cranking.

Results:

• OK - The sensor is producing the correct output signal.

  Repair: Remove the breakout t from the connectors for the speed/timing sensor. Reconnect the connectors for the speed/timing sensor.

  Proceed to Test Step 8.

• Not OK - The sensor is not producing the correct output signal.

  Repair: Set the engine control to the OFF/RESET mode. Switch the 35 amp circuit breaker OFF.

  Remove the breakout t from the connectors for the speed/timing sensor.

  Install a new speed/timing sensor. Calibrate the sensor. Refer to Troubleshooting, "Timing - Calibrate".

  STOP

Test Step 7. Measure the Sensor Supply Voltage at the ECM

1. Set the engine control to the OFF/RESET mode.

2. Use two 7X-1710 Multimeter Probes. Insert the probes into terminals P1-33 and P1-51.

3. Set the engine control to the STOP mode. Measure the supply voltage at the ECM.

Expected Result:

The voltage is between 11.5 VDC and 13.5 VDC. A 145-3 diagnostic code or a 145-4 diagnostic code is not active.

Results:

• Yes - The sensor supply voltage at the ECM is between 11.5 VDC and 13.5 VDC. A 145-3 diagnostic code or a 145-4 diagnostic code is not active. The wiring and/or the connectors between the sensor and the ECM has an open circuit or the circuit has excessive resistance.

  Repair: Set the engine control to the OFF/RESET mode. Switch the 35 amp circuit breaker OFF. Make the necessary repairs to the harness and/or connectors.

  STOP

• No - The ECM is not producing the correct sensor supply voltage or a 145-3 or a 145-4 diagnostic code is active. There may be a problem with the ECM.

  Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If the condition is not resolved, perform the following steps:

  Temporarily install a new ECM. Refer to Troubleshooting, "ECM - Replace".

  If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the ECM. Refer to Troubleshooting, "ECM - Replace".

  STOP

Test Step 8. Isolate the Sensor Signal at the ECM and Measure the Sensor Signal Voltage at the ECM

1. Set the engine control to the OFF/RESET mode.

2. Use a 151-6320 Wire Removal Tool to remove terminals P1-33 and P1-51.

3. Connect the leads of a multimeter to the terminals that were removed from the P1 connector.

4. Set the engine control to the STOP mode. Measure the signal voltage between the terminals. Record the measurement.

5. Set the engine control to the START mode. Crank the engine and measure the signal voltage between the terminals again. Record the measurement.

Expected Result:

When the engine control is in the STOP mode, the voltage is less than 3.0 VDC or the voltage is greater than 10.0 VDC.

The voltage varied between 2.0 VDC and 4.0 VDC during cranking.

Results:

• OK - Both of the measurements are correct. However, the ECM is not reading the signal. There may be a problem with the ECM.

  Repair: Temporarily install a new ECM. Refer to Troubleshooting, "ECM - Replace".

  If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the ECM. Refer to Troubleshooting, "ECM - Replace".

  STOP

• Not OK - The signal voltage is not correct. There is an intermittent problem in the circuit for the speed/timing sensor.

  Repair: Refer to Troubleshooting, "Electrical Connectors - Inspect". Make repairs, as needed.

  STOP