3176C, 3406E and 3456 Industrial Engines Troubleshooting – Speed/Timing – Test

System Operation Description:

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

Table 1

Diagnostic Codes Table
Code and Description	Conditions which Generate this Code	System Response
190-2 Engine Speed Sensor : Erratic, Intermittent, or Incorrect	The signal from the engine speed/timing sensor has been lost. The code is logged only if the engine has been running for three seconds.	The code is logged. The Electronic Control Module (ECM) will default to the secondary engine speed/timing sensor. If a valid signal is not received from the engine speed/timing sensor the engine will shut down.
190-3 Engine Speed Sensor : Voltage Above Normal	The signal wire for the primary engine speed/timing sensor is above normal.	The code is logged. The engine will shut down.
190-7 Engine Speed Sensor : Not Responding Properly	The primary engine speed/timing sensor is connected to the harness connector for the secondary engine speed/timing sensor.	The code is logged. The engine will shut down. Check for the correct installation of the sensors.
190-8 Engine Speed Sensor : Abnormal Frequency, Pulse Width, or Period	The signal from the engine speed/timing sensor has been incorrect for at least five seconds.	The code is logged. The ECM will default to the secondary engine speed/timing sensor. If a valid signal is not received from the engine speed/timing sensor the engine will shut down.
342-2 Secondary Engine Speed Sensor : Erratic, Intermittent, or Incorrect	The signal from the engine speed/timing sensor has been lost. The code is logged only if the engine has been running for three seconds.	The code is logged. The ECM will default to the secondary engine speed/timing sensor. If a valid signal is not received from the engine speed/timing sensor the engine will shut down.
342-3 Secondary Engine Speed Sensor : Voltage Above Normal	The signal wire for the primary engine speed/timing sensor is above normal.	The code is logged. The engine will shut down.
342-7 Secondary Engine Speed Sensor : Not Responding Properly	The primary engine speed/timing sensor is connected to the harness connector for the secondary engine speed/timing sensor.	The code is logged. The engine will shut down. Check for the correct installation of the sensors.
342-8 Secondary Engine Speed Sensor : Abnormal Frequency, Pulse Width, or Period	The signal from the engine speed/timing sensor has been incorrect for at least five seconds.	The code is logged. The ECM will default to the secondary engine speed/timing sensor. If a valid signal is not received from the engine speed/timing sensor the engine will shut down.

The engine uses two engine speed/timing sensors. Both sensors detect the reference for engine speed and timing from a timing reference ring with a unique pattern. The ECM uses the pattern of the pulses in order to determine the position of the crankshaft. The ECM measures the time between the pulses that are created by the sensors as the gears rotate in order to determine rpm.

Under normal operation, the primary speed/timing sensor determines when the piston in the number one cylinder is at the top of the compression stroke. When the timing has been established, the sensor signal is used to determine engine speed.

When the timing has been established, the ECM triggers each injector in the correct firing order at the correct time. The actual timing and duration of each injection is based on engine rpm and on load.

The secondary speed/timing sensor provides continuous operation of the engine if the primary engine speed/timing sensor fails. If the engine is running and the signal from one sensor is lost, no change in engine performance will be noticed. If the engine is running and the signals from both sensors are lost, fuel injection will be terminated and the engine will be shut down by the ECM.

The engine will start when only one sensor signal is present. The engine will not start if the signals from both sensors are lost.

The engine speed/timing sensors receive supply voltage from the ECM that is regulated at 12.5 ± 1.0 VDC. The engine speed/timing sensors provide a pulsed DC output voltage with a frequency that is directly proportional to engine speed. A unique tooth on the timing reference ring generates a duty cycle in order to provide the ECM with information on the crankshaft position.

Illustration 1 g01429128
Typical schematic for the engine speed/timing sensors

Test Step 1. Inspect the Electrical Connectors and the Wiring

 

1. Remove electrical power from the ECM.

Illustration 2 g01408680
ECM

(1) J1/P1 connectors

(2) J2/P2 connectors

2. Thoroughly inspect the J2/P2 and the J1/P1ECM connectors. Inspect all of the connectors that are associated with the circuit.Refer to Troubleshooting, “Electrical Connectors – Inspect” for details.

Illustration 3 g01408682
P2 ECM connector

(P2-1) Supply for the speed/timing sensor

(P2-4) Timing calibration probe –

(P2-29) Return

(P2-37) Signal for the primary speed/timing sensor

(P2-39) Timing calibration probe +”Timing calibration probe +”

Illustration 4 g01429185
P1 ECM connector

(P1-18) Signal for the secondary speed/timing sensor

3. Perform a 45 N (10 lb) pull test on each of the wires in the circuit.

 

4. Check the allen head screw from each ECM connector for the proper torque. Refer to Troubleshooting, “Electrical Connectors – Inspect” for the correct torque value.

 

5. Check the harness and the wiring for abrasion and for pinch points.

Expected Result:

All of the connectors, pins and sockets are completely coupled and/or inserted and the harness and wiring are free of corrosion, of abrasion and of pinch points.

Results:

 

• OK – The harness and connectors appear to be OK. Proceed to Test Step 2. 
• Not OK – The connectors and/or wiring are not OK.Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check for Diagnostic Codes

 

1. Connect the Caterpillar Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, “Electronic Service Tools”.

 

2. Restore electrical power to the ECM.

 

3. Check for active diagnostic codes on Cat ET.Look for one of the following codes:

    

   • 190-2 
   • 190-3 
   • 190-7 
   • 190-8 
   • 342-2 
   • 342-3 
   • 342-7 
   • 342-8 

Expected Result:

None of the above diagnostic codes are active.

Results:

 

• OK – None of the above codes are active, but there is a problem that has been associated with the engine speed/timing sensors. Proceed to Test Step 3. 
• OK – None of the above diagnostic codes is logged or active.Repair: There may be an intermittent problem in the circuit. If an intermittent problem is suspected, refer to Troubleshooting, “Electrical Connectors – Inspect”.

  STOP

   

• Not OK – One or more of the above codes are active. Proceed to Test Step 3.

Test Step 3. Inspect the Condition of the Engine Speed/Timing Sensors

 

1. Remove the suspect engine speed/timing sensor.

 

2. Inspect the sensor tip for damage.

 

3. Inspect the plastic sliphead for damage.

 

4. Check the tension on the sliphead by gently prying the sliphead out of the sensor body. Extend the sliphead 3 to 4 mm (0.12 to 0.16 inch). Push the sliphead back into the sensor body from the extended position. Movement of the sliphead will require a small amount of force. The amount of tension that is on the sliphead must not allow movement of the sliphead during engine operation.

 

5. If the sensor is not damaged, pull the sliphead from the sensor body to the fully extended position and reinstall the sensor.Note: Be sure to extend the sliphead before installing the engine speed/timing sensor. Ensure that the timing gear is in a position that will not allow the sliphead to protrude into one of the slots of the timing gear during installation. Turn the crankshaft in order to rotate the timing gear to a position that will not allow the sliphead to protrude into a slot. If the sliphead protrudes into one of the slots of the timing gear, the sliphead will be damaged as the timing gear begins to rotate.

Expected Result:

The sensor is not damaged. An adequate amount of tension is felt on the sliphead and the movement is smooth.

Results:

 

• OK – The engine speed/timing sensor and the sliphead are undamaged. The tension on the sliphead is normal.Repair: Reinstall the engine speed/timing sensor. Ensure that the timing gear is positioned correctly prior to installing the sensor.

  Proceed to Test Step 4.

   

• Not OK – The engine speed/timing sensor or the sliphead is damaged.Repair: Replace the engine speed/timing sensor.

  STOP

Test Step 4. Check the Engine Speed on Cat ET

 

1. Restore electrical power to the ECM. Start the engine.

 

2. Observe the engine speed on Cat ET while the engine is cranking.

Expected Result:

Cat ET displays a steady engine speed between 100 and 250 rpm while the engine is cranking and the engine starts.

Results:

 

• OK – The engine speed/timing sensor is operating normally at this time.Repair: If you are troubleshooting an intermittent problem, refer to Troubleshooting, “Electrical Connectors – Inspect”.

  STOP

   

• Not OK – Cat ET displays zero engine speed and the engine does not start. Proceed to Test Step 5. 
• Not OK – Cat ET displays a steady engine speed, but the engine will not start.Repair: Proceed to Troubleshooting, “Engine Cranks But Does Not Start”.

  STOP

Test Step 5. Check the Supply Voltage at the Sensor Connector

 

1. Disconnect the connector for the suspect engine speed/timing sensor.

 

2. Measure the voltage between terminal A and terminal B at the suspect sensor connector.

 

3. Remove electrical power from the ECM.

Expected Result:

The supply voltage is measured at 11.5 to 13.5 VDC at the sensor connector.

Results:

 

• OK – The engine speed/timing sensor is receiving the correct supply voltage. Proceed to Test Step 6. 
• Not OK – The supply voltage is not within the specified range. Proceed to Test Step 7.

Test Step 6. Check the Isolated Signal Voltage at the Sensor

 

1. Remove the wire from terminal C (speed/timing sensor signal) at the harness side of the connector for the suspect speed/timing sensor.

 

2. Reconnect the suspect sensor at the sensor connector.

 

3. Measure the voltage between the suspect sensor signal wire and terminal B of the suspect sensor connector. Also, crank the engine and measure the voltage between the suspect sensor signal wire and terminal B during engine cranking.

 

4. Remove electrical power from the ECM.

 

5. Restore the wiring to the original configuration.

Expected Result:

The voltage is less than 2 VDC or the voltage is greater than 10 VDC when the ECM is powered and the engine is not cranking. The voltage varies between 2 VDC and 9 VDC during engine cranking.

Results:

 

• OK – The engine speed/timing sensor is producing an output signal. Proceed to Test Step 8. 
• Not OK – The engine speed/timing sensor is not producing a valid output signal.Repair: Replace the engine speed/timing sensor. Calibrate the sensor. Perform the calibration procedure Troubleshooting, “Timing – Calibrate”.

  STOP

Test Step 7. Check the Supply Voltage at the ECM

 

1. Disconnect the J2/P2 ECM connector.

 

2. Fabricate two jumper wires that are long enough to be used as a test circuit at the ECM connector. Crimp a connector socket to one end of each of the jumper wires.

 

3. Remove the wire from terminal location P2-29 at the ECM connector. Install one of the jumper wires into terminal location P2-29.

 

4. Remove the wire from terminal location P2-1 at the ECM connector. Install one of the jumper wires into terminal location P2-1.

 

5. Connect the J2/P2 ECM connector.

 

6. Restore electrical power to the ECM.

 

7. Measure the supply voltage between the jumper wires in terminal locations P2-29 and P2-1.

 

8. Remove electrical power from the ECM.

 

9. Restore the wiring to the original configuration.

Expected Result:

The voltage is 12.5 ± 1.0 VDC.

Results:

 

• OK – The voltage is 12.5 ± 1.0 VDC.Repair: There is a problem in the harness wiring between the ECM and the connector for the engine speed/timing sensor. Repair the connectors and/or wiring or replace the connectors and/or wiring.

  STOP

   

• Not OK – The voltage is not 12.5 ± 1.0 VDC.Repair: Ensure that the ECM is receiving the correct supply voltage from the batteries. Refer to Troubleshooting, “Electrical Power Supply – Test”.If the ECM is receiving the correct supply voltage, replace the ECM. Refer to Troubleshooting, “ECM – Replace”.

  STOP

Test Step 8. Check the Signal Voltage at the ECM

 

1. Disconnect the J2/P2 or the J1/P1 ECM connector.

 

2. Remove the signal wire for the suspect sensor from the ECM connector. Refer to Illustration 1 for the correct wire for the suspect sensor.

 

3. Reconnect the ECM connector.

 

4. Measure the signal voltage between the signal wire and engine ground.

 

5. Crank the engine and measure the signal voltage between the signal wire and engine ground.

 

6. Remove electrical power from the ECM.

 

7. Restore the wiring to the original configuration.

Expected Result:

The voltage measures less than 2 VDC or more than 10 VDC when the ECM is powered and the engine is not cranking. While the engine is cranking, the voltage is between 2 VDC and 9 VDC.

Results:

 

• OK – The correct voltage is measured on the signal wire that was removed from the ECM connector.Repair: The ECM does not appear to be reading the signal. Replace the ECM. Refer to the diagnostic procedure Troubleshooting, “ECM – Replace”.

  STOP

   

• Not OK – The voltage is incorrect on the signal wire that was removed from the ECM connector.Repair: The problem is in the harness between the ECM and the engine speed/timing sensor. Repair the connectors and/or wiring or replace the connectors and/or wiring.

  STOP