C9 Urban Transit Bus Engine Caterpillar

Use this procedure under the following situation:

Use this procedure to troubleshoot the system only when there is an active diagnostic code or when a diagnostic code can easily be activated. This procedure covers open circuit diagnostic codes and short circuit diagnostic codes that are associated with the following sensors:

• Coolant temperature sensor

• Air inlet temperature sensor

Use this procedure for the following Diagnostic Codes:

• 105-03 Intake Manifold Air Temperature voltage high (38)

• 105-04 Intake Manifold Air Temperature voltage low (38)

• 110-03 Coolant Temperature voltage high (27)

• 110-04 Coolant Temperature voltage low (27)

The following background information is related to this procedure:

The troubleshooting procedures for the diagnostic codes of each temperature sensor are identical. The temperature sensors are passive sensors that have two terminals. The passive sensors do not require supply voltage from the ECM. ECM connector J2/P2 terminal 18 is the common connection for the engine temperature sensors. The sensor common connection is shared between all of the temperature sensors. The common line is connected to each sensor connector terminal 2. Terminal 1 is the sensor output. The signal from terminal 1 of each sensor is supplied to the appropriate terminal at ECM connector J2/P2.

Illustration 1	g00924851
Left side view of the engine

Illustration 2	g00724478
Schematic for engine temperature sensors

Test Step 1. Inspect Electrical Connectors and Wiring

Illustration 3	g00864872
Pin Locations on the ECM connector P2

1. Thoroughly inspect the J2/P2 ECM connector and the suspect sensor connector. Refer to Troubleshooting, "Electrical Connections - Inspect" for details.

2. Perform a 45 N (10 lb) pull test on each of the wires in the sensor connector and the ECM connector that are associated with the active diagnostic code.

   Refer to Illustration 3.

3. Verify that the latch tab of the connector is properly latched and that the latch tab of the connector has returned to the Fully Latching position.

4. Check the ECM Connector (allen head screw) for the proper torque of 6.0 N·m (55 lb in).

5. Check the harness and wiring for abrasion and pinch points from the sensor to the ECM.

Expected Result:

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

Results:

• OK - Proceed to Test Step 2.

• 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. Determine the Condition that is Present

1. Connect the Caterpillar Electronic Technician (Cat ET) to the data link connector.

2. Turn the key switch to the ON position. Wait at least 15 seconds for activation of the diagnostic codes.

3. Check for active diagnostic codes on Cat ET.

4. Determine if the problem is related to a "voltage high" diagnostic code (open circuit) or a "voltage low" diagnostic code (short circuit).

Expected Result:

A "voltage high" diagnostic code (open circuit) or a "voltage low" diagnostic code (short circuit) is active.

Results:

• Voltage High (Open) - A "voltage high" diagnostic code (open circuit) is active at this time. Proceed to Test Step 6.

• Voltage Low (Short) - A "voltage low" diagnostic code (short circuit) is active at this time. Proceed to Test Step 3.

Test Step 3. Disconnect the Suspect Sensor

1. Turn the key switch to the OFF position.

2. Disconnect the sensor with the "voltage low" diagnostic code (short circuit).

3. Turn the key switch to the ON position. Wait at least 15 seconds for activation of the diagnostic codes.

4. Check for an active "voltage high" diagnostic code (open circuit) on Cat ET.

Expected Result:

A "voltage high" diagnostic code (open circuit) for the suspect sensor is now active.

Results:

• OK - A "voltage high" diagnostic code (open circuit) for the suspect sensor is now active.

  Repair: Temporarily connect a new sensor.If the new sensor fixes the problem, reconnect the suspect sensor.If the problem returns, permanently replace the sensor.Verify that the repair eliminates the problem.

  Stop.

• Not OK - There is a short circuit between the sensor harness connector and the ECM.

  Repair: Leave the sensor disconnected.

  Proceed to Test Step 4.

Test Step 4. Disconnect the ECM Connector

1. Turn the key switch to the OFF position.

2. Disconnect the J2/P2 ECM connector. Thoroughly inspect both halves of the connector for signs of corrosion or moisture.

   Note: If the Ambient Air Temperature Sensor is being tested, a 140-2266 Cable (Seventy-Pin Breakout) is required in order to maintain the battery connections.

3. Turn the key switch to the ON position. Wait at least 15 seconds for activation of the code.

4. Check for active diagnostic codes on Cat ET.

   Note: When the J2/P2 ECM connector is disconnected, all of the "voltage high" diagnostic codes (open circuit) for the temperature sensors will be active. This is normal.

Expected Result:

"Voltage high" diagnostic codes (open circuit) are active when the J2/P2 ECM connector is disconnected.

Results:

• OK - The ECM is working properly.

  Repair: Leave the ECM connector disconnected.

  Proceed to Test Step 5.

• Not OK - A "voltage low" diagnostic code (short circuit) is still active for the suspect sensor.

  Repair: Temporarily connect a test ECM.If the test ECM fixes the problem, reconnect the suspect ECM.If the problem returns, permanently replace the suspect ECM.Verify that the repair eliminates the problem.

  Stop.

Test Step 5. Check the Resistance

1. Turn the key switch to the OFF position.

2. Verify that the suspect sensor and the ECM connector are disconnected.

3. Measure the resistance between terminal 1 and terminal 2 of the sensor connector.

Expected Result:

The resistance is greater than 20,000 ohms or "OL" is displayed on the multimeter.

Results:

• OK - There is a problem with the supply wire.

  Repair: Check the supply wire of the suspect sensor for a short to ground.Repair the faulty wiring or replace the faulty wiring.Verify that the repair eliminates the problem.

  Stop.

• Not OK - There is a short between the supply wire and the common wire.

  Repair: Locate the short between the supply wire and the common wire.Repair the faulty wiring or replace the faulty wiring.Verify that the repair eliminates the problem.

  Stop.

Test Step 6. Create a Short at the Sensor

1. Fabricate a jumper wire 150 mm (6 inch) long.

2. Turn the key switch to the ON position.

3. Monitor the active diagnostic code screen.

4. Install the jumper wire between terminal 1 and terminal 2 of the sensor connector.

Expected Result:

A "voltage low" diagnostic code (short circuit) is active when the jumper wire is installed.

Results:

• OK - A "voltage low" diagnostic code (short circuit) is active.

  Repair: Temporarily connect a new sensor.If the new sensor fixes the problem, reconnect the suspect sensor.If the problem returns, permanently replace the suspect sensor.Verify that the repair eliminates the problem.

  Stop.

• Not OK - A "voltage high" diagnostic code (open circuit) is still active.

  Repair: Remove the jumper wire.

  Proceed to Test Step 7.

Test Step 7. Create a Short at the ECM

Illustration 4	g00767376
Engine harness connector

1. Turn the key switch to the OFF position.

2. Disconnect the P2 ECM connector.

3. Fabricate a jumper wire 150 mm (6 inch) long.

4. Install the jumper wire between the terminal for the sensor supply of the suspect sensor and the terminal for the sensor common.

Expected Result:

A "voltage low" diagnostic code (short circuit) is active when the jumper wire is installed.

Results:

• OK - A "voltage low" diagnostic code (short circuit) is active when the jumper wire is installed.

  Repair: Reconnect the P2 ECM connector.

• Not OK - A "voltage high" diagnostic code (open circuit) is still active.

  Repair: Temporarily connect a test ECM.If the test ECM fixes the problem, reconnect the suspect ECM.If the problem returns, permanently replace the suspect ECM.Verify that the repair eliminates the problem.

  Stop.

Test Step 8. Check the Voltage at the Sensor

1. Turn the key switch to the ON position.

2. Verify that the sensor is disconnected.

3. Measure the voltage between terminal 1 of the sensor connector and chassis ground.

Expected Result:

The voltage should be 5.0 ± 0.5 volts.

Results:

• OK - The voltage is within the range.

  Repair: Check for an open circuit in the common wire.Repair the faulty wiring or replace the faulty wiring.Verify that the repair eliminates the problem.

  Stop.

• Not OK - The voltage is not within the range.

  Repair: If the voltage is above 5.5 VDC, check the supply wire for a short to a voltage source.If the voltage is below 4.5 VDC, check the supply wire for an open circuit.Repair the faulty wiring or replace the faulty wiring.Verify that the repair eliminates the problem.

  Stop.