C7.1 Engines Caterpillar


Valve Position - Test

Usage:

C7.1 881
This procedure covers the following diagnostic codes:

Table 1
Diagnostic Codes for the Valve Position Sensors 
J1939 Code  CDL Code  Code Description
(code descriptions may vary) 
Comments 
27-3  3407-3  EGR #1 Valve Position : Voltage Above Normal  The Electronic Control Module (ECM) detects the following conditions:

The signal voltage from the position sensor on the NOx Reduction System (NRS) valve is greater than 4.8 VDC for 0.1 seconds.

The warning lamp will come on. The ECM will log the diagnostic code. The NRS valve will be fully closed while the code is active.
The engine will be derated. 
27-4  3407-4  EGR #1 Valve Position : Voltage Below Normal  The ECM detects the following conditions:

The signal voltage from the NRS valve position sensor is less than 0.2 VDC for 0.1 seconds.

The warning lamp will come on. The ECM will log the diagnostic code. The NRS valve will be fully closed while the code is active.
The engine will be derated. 
5625-3  3513-3  Engine Exhaust Back Pressure Regulator Position : Voltage Above Normal  The ECM detects the following conditions:

The signal voltage from the position sensor on the exhaust back pressure regulator is greater than 4.8 VDC for 0.1 seconds.

The warning lamp will come on. The ECM will log the diagnostic code. The engine exhaust back pressure regulator will be fully open while the code is active.
The engine will be derated. 
5625-4  3513-4  Engine Exhaust Back Pressure Regulator Position : Voltage Below Normal  The ECM detects the following conditions:

The signal voltage from the position sensor on the exhaust back pressure regulator is less than 0.2 VDC for 0.1 seconds.

The warning lamp will come on. The ECM will log the diagnostic code. The exhaust back pressure regulator will be fully open while the code is active.
The engine will be derated. 
Follow the troubleshooting procedure in order to identify the root cause of the fault. 

The following conditions must exist before any of the preceding codes will become active:

  • The ECM has been powered for at least 2 seconds.

  • There are no active 168 codes.

  • There are no active 3509 or 262 codes.

Use this procedure in order to troubleshoot the position sensors for the following valves:

  • NRS valve

  • Exhaust back pressure regulator

Each position sensor is integral in the associated valve. If the following procedure indicates a fault with the position sensor, then the entire valve must be replaced.

The following background information is related to this procedure:

The troubleshooting procedures for the diagnostic codes of each position sensor are identical. The 5 VDC sensor supply provides power to all 5 VDC sensors. The ECM supplies 5.0 VDC to terminal "1" of both valve connectors. The sensor common from the ECM connector goes to terminal "2" of both valve connectors. The sensor supply is output short circuit protected. A short circuit to the battery will not damage the circuit inside the ECM. The signal voltage from terminal "3" of both valves is supplied to the appropriate terminal at the P2 ECM connector.

Pull-up Voltage

The ECM continuously outputs a pull-up voltage on the circuit for the sensor signal wire. The ECM uses this pull-up voltage in order to detect an open in the signal circuit. When the ECM detects a voltage above a threshold, the ECM generates an open circuit diagnostic code (XXXX-3).

If the sensor is disconnected, pull-up voltage indicates that the wires are not open or shorted to ground. The absence of pull-up voltage indicates an open in the signal wire or a short to ground. If the voltage is different from pull-up voltage, the signal wire is shorted to another wire in the harness.



Illustration 1g03812374
Schematic diagram for the valve position sensors


Illustration 2g03812375
Pin locations on the P2 connector for the valve position sensors
(1) Valve position sensor 5 VDC supply
(10) Valve position sensors ground
(30) Combustion air valve position sensor signal
(38) NRS valve position sensor signal


Illustration 3g03177615
Connector for the NRS valve
(1) 5 VDC supply
(2) Position sensor ground
(3) Position sensor signal


Illustration 4g03177636
Connector for the exhaust back pressure regulator
(1) 5 VDC supply
(2) Position sensor ground
(3) Position sensor signal

Complete the procedure in the order in which the steps are listed.

Table 2
Troubleshooting Test Steps  Values  Results 

1. Inspect Electrical Connectors and Wiring

A. Turn the keyswitch to the OFF position.

B. Inspect the connectors for the valve position sensors. Refer to Troubleshooting, "Electrical Connectors - Inspect".

C. Perform a 45 N (10 lb) pull test on each of the wires in the suspect sensor connector and the sensor connections at the ECM.

D. Check the screw for the J2 ECM connector for the correct torque of 6 N·m (53 lb in).

E. Check the ground connection on the ECM for abrasions and pinch points.

F. Check the harness for abrasion and pinch points from the suspect sensor to the ECM.
 

Loose connection or damaged wire
 

Result: There is a fault in a connector or the wiring.

Repair: Repair any faulty connectors or replace the wiring harness. Ensure that all of the seals are properly in place and ensure that the connectors are correctly coupled.

Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.

Result: All connectors, pins, and sockets are correctly coupled and/or inserted. The harness is free of corrosion, abrasion, and pinch points.

Proceed to Test Step 2.
 

2. Check For Active Diagnostic Codes

A. Turn the keyswitch to the OFF position.

B. Connect the electronic service tool to the diagnostic connector.

C. Turn the keyswitch to the ON position. Wait at least 10 seconds for activation of the diagnostic codes.

D. Use the electronic service tool in order to monitor active diagnostic codes or recently logged diagnostic codes.

E. Turn the keyswitch to the OFF position.
 

Diagnostic codes
 

Result: One or more of the preceding diagnostic codes are active or recently logged.

Proceed to Test Step 3.

Result: None of the preceding diagnostic codes are active or recently logged.

Repair: The fault may be intermittent. Refer to Troubleshooting, "Electrical Connectors - Inspect".

Perform a "Wiggle Test" by using the electronic service tool in order to identify intermittent connections.
 

3. Measure the Supply Voltage at the Valve Connector

A. Turn the keyswitch to the OFF position.
B. Disconnect the suspect valve from the harness.

C. Turn the keyswitch to the ON position.

D. Measure the voltage between terminals 1 and 2 at the connector for the valve.

E. Reconnect the valve to the harness.
 

4.84 to 5.16 VDC
 

Result: The sensor supply voltage is out of the nominal range. The fault is in the engine harness between the valve connector and the ECM.

Repair: Repair the faulty valve connector or replace the faulty harness.

Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.

Result: The sensor supply voltage is correct.

Proceed to Test Step 4.
 

4. Verify that the Diagnostic Code is Still Active

A. Turn the keyswitch to the ON position. Wait at least 10 seconds for activation of the diagnostic codes.

B. Use the electronic service tool to check for active diagnostic codes. Record all active diagnostic codes.
 

Diagnostic codes
 

Result: An XXXX-4 diagnostic code is active at this time.

Proceed to Test Step 5.

Result: An XXXX-3 diagnostic code is active at this time.

Proceed to Test Step 7.

Result: No diagnostic codes are active at this time. An intermittent fault may exist.

Repair: Use the electronic service tool to perform a "Wiggle Test". If faults are indicated, then go to the appropriate procedure.
 

5. Create an Open Circuit at the Valve Connector

A. Turn the keyswitch to the OFF position.

B. Disconnect the connector for the valve with the XXXX-4 diagnostic code.

C. Remove the wire for the position sensor signal from the harness connector for the valve.

D. Reconnect the connector for the valve.

E. Turn the keyswitch to the ON position. Wait for at least 10 seconds for activation of the diagnostic codes.

F. Use the electronic service tool to check the "Active Diagnostic Code" screen. Check for an XXXX-3 diagnostic code.

G. Turn the keyswitch to the OFF position.
 

Open circuit
 

Result: An XXXX-4 diagnostic code was active before removing the signal wire. An XXXX-3 diagnostic code became active after removing the signal wire.

Repair: Disconnect the connector for the valve.

Reconnect the signal wire for the position sensor. Reconnect the connector for the valve.

Turn the keyswitch to the ON position. Use the electronic service tool to check for active diagnostic codes. If the XXXX-4 diagnostic code returns, there is a short in the valve.

Install a replacement valve. Refer to Disassembly and Assembly for the correct procedure.

Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.

Result: There is still an XXXX-4 diagnostic code active with the signal wire removed. The valve position sensor is OK.

Repair: Return all wires to the original configuration. Proceed to Test Step 6.
 

6. Check the Harness for a Short Circuit

A. Turn the keyswitch to the OFF position.

B. Disconnect the P2 ECM connector and the connector for the suspect valve.

C. For a suspect NRS valve position sensor, measure the resistance between P2:38 and all other terminals on P2.

D. For a suspect EBPR position sensor, measure the resistance between P2:30 and all other terminals on P2.

E. Install the removed connectors.
 

Greater than 100 Ohms
 

Result: The measured resistance is less than 100 Ohms. There is a short circuit in the harness.

Repair: Repair the valve connector or replace the harness.

Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.

Result: The measured resistance is greater than 100 Ohms.

Contact the Dealer Solutions Network (DSN).
 

7. Create a Short Circuit at the Valve Connector

A. Turn the keyswitch to the OFF position.

B. Disconnect the connector for the valve with the XXXX-3 diagnostic code.

C. Fabricate a jumper wire that is 150 mm (6 inch) long.

D. Insert one end of the jumper wire into terminal 3 on the harness connector for the suspect valve. Insert the other end of the jumper into terminal 2.

E. Turn the keyswitch to the ON position.

F. Access the "Active Diagnostic Codes" screen on the electronic service tool and check for an active XXXX-4 diagnostic code for the suspect sensor.

G. Remove the jumper.
 

Less than two Ohms
 

Result: An XXXX-3 diagnostic code was active before the jumper was installed. An XXXX-4 diagnostic code is active when the jumper is installed.

Repair: Reconnect the connector for the suspect valve.

Turn the keyswitch to the ON position. Use the electronic service tool to check for active diagnostic codes. If the XXXX-3 diagnostic code returns, there is an open circuit in the valve. Install a replacement valve. Refer to Disassembly and Assembly for the correct procedure.

Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.

Result: An XXXX-3 diagnostic code remains active when the jumper is installed. The valve is OK.

Proceed to Test Step 8.
 

8. Check the Wiring Harness for an Open Circuit

A. Turn the keyswitch to the OFF position.

B. Disconnect the P2 ECM connector and the connector for the suspect valve.

C. For a suspect NRS valve, check the resistance between terminal 3 on the valve connector and P2:38.

D. For a suspect exhaust back pressure regulator, check the resistance between terminal 3 on the valve connector and P2:30.

E. Install the removed connectors.
 

Less than two Ohms
 

Result: The measured resistance is greater than two Ohms. There is an open circuit in the harness.

Repair: Repair the valve connector or replace the harness.

Use the electronic service tool to clear all logged diagnostic codes and verify that the repair eliminates the fault.

Result: The measured resistance is less than two Ohms.

Contact the Dealer Solutions Network (DSN).
 

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