G3600 A4 Engines Air/Fuel Pressure Module - Test - G3616 Caterpillar


Air/Fuel Pressure Module - Test - G3616
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Use this procedure to troubleshoot a problem with the air/fuel pressure module. Also, use this procedure if one of the following diagnostic codes is active or easily repeated.

Table 1
J1939 Code and Description  Comments 
1392-3
Engine Air to Fuel Differential Pressure : Voltage Above Normal 
An open circuit has been detected.
The code is logged. 
1392-4
Engine Air to Fuel Differential Pressure : Voltage Below Normal 
A short circuit has been detected.
The code is logged. 
1392-8
Engine Air to Fuel Differential Pressure : Abnormal Frequency, Pulse Width, or Period 
The frequency of the pressure sensor is outside the range of the sensor.
The code is logged. 
4817-3
Engine Intake Manifold #1 Absolute Pressure : Voltage Above Normal 
An open circuit has been detected.
The code is logged. 
4817-4
Engine Intake Manifold #1 Absolute Pressure : Voltage Below Normal 
A short circuit has been detected.
The code is logged. 
4817-8
Engine Intake Manifold #1 Absolute Pressure : Abnormal Frequency, Pulse Width, or Period 
The frequency of the pressure sensor is outside the range of the sensor.
The code is logged. 

Tubes that connect the air/fuel pressure module to the inlet air manifold and to the fuel manifold enable the module to sense the absolute inlet manifold air pressure and fuel pressure. The module calculates the differential pressure between the fuel manifold and the inlet air manifold. This fuel differential pressure is the value of the fuel pressure minus the value of the inlet manifold air pressure.

Pulse Width Modulation (PWM) - This is a digital signal. The frequency is constant: the percent on time versus the period is called a duty cycle. If the signal is on for 50 percent of the period as an example, the duty cycle is 50 percent. This provides a more accurate status for a parameter than a signal that can only be ON or OFF.

The air/fuel pressure module sends PWM signals that represent the inlet manifold air pressure and the fuel differential pressure to the Electronic Control Module (ECM). The ECM uses the information to help calculate the fuel flow.



Illustration 1g03788049

Table 2
Troubleshooting Test Steps  Values  Results 

1. Check for Codes

A. Connect Cat® Electronic Technician (ET) to the service tool connector.

B. Determine if a code is active or logged.
 

Codes
 

Result: A -3 code is active or logged.

Proceed to Test Step 2.

Result: A -4 code is active or logged.

Proceed to Test Step 3.

Result: A -8 code is active or logged.

Proceed to Test Step 5.
 

2. Create a Short at the Sensor Connector

A. Turn the main disconnect switch to the OFF position.

B. Disconnect the sensor with the active -3 code.

C. Install the jumper wire between the following terminals at the air/fuel pressure module wiring harness connector:

- Affected sensor signal terminal and Terminal B (sensor return)

D. Connect Cat ET.

E. Use Cat ET to monitor the following:

- -4 code

F. Turn the main disconnect switch to the OFF position.
 

Create a Short
 

Result: A -4 code became active.

Repair: The wiring harness is OK. Replace the sensor.

Verify that the repair eliminated the problem.

Result: A -4 code did not become active.

Proceed to Test Step 4.
 

3. Create an Open at the Sensor Connector

A. Turn the main disconnect switch to the OFF position.

B. Disconnect the air/fuel pressure module.

C. Connect Cat ET.

D. Use Cat ET to monitor the following:

- -3 code

F. Turn the main disconnect switch to the OFF position.
 

Create an Open
 

Result: A -3 code became active.

Repair: The wiring harness is OK. Replace the air/fuel pressure module.

Verify that the repair eliminated the problem.

Result: A -3 code did not become active.

Proceed to Test Step 4.
 

4. Check the 24 VDC Supply Voltage at the Sensor Connector

A. Turn the main disconnect switch to the ON position.

B. Measure the voltage at the following terminal locations at the air/fuel pressure module connector:

- Terminal A and Terminal B

C. Reconnect the air/fuel pressure module.
 

Supply Voltage
 

Result: The supply voltage is approximately battery voltage.

Proceed to Test Step 8.

Result: The supply voltage is not approximately battery voltage.

Repair: There is a short in the wiring harness to the battery. Repair or replace the wiring harness.

If the problem is not resolved, proceed to Test Step 5.
 

5. Check the PWM Circuit for an Open

A. Turn the main disconnect switch to the OFF position.

B. Disconnect the air/fuel pressure module.

C. Disconnect the J1 connector at the ECM.

D. Measure the resistance between the following terminal locations for the air/fuel pressure module:

- The signal wire at the affected sensor terminal and the appropriate PWM signal wire on the ECM connector
 

Open Circuit
 

Result: Less than 10 ohms of resistance between the sensor connector and the ECM connector.

Proceed to Test Step 6.

Result: More than 10 ohms of resistance between the sensor connector and the ECM connector.

There is an open circuit in the wiring harness. Repair or replace the wiring harness.

If the problem is not resolved, proceed to Test Step 6.
 

6. Check the PWM Circuit for a Short Circuit

A. Turn the main disconnect switch to the OFF position.

B. Disconnect the air/fuel pressure module.

C. Disconnect the J1 connector at the ECM.

D. Measure the resistance between the following locations for the sensor:

- The signal wire at the affected sensor terminal and Engine ground
 

Short Circuit
 

Result: There was more than 100 K ohms of resistance between The signal wire at the affected sensor terminal and engine ground.

Proceed to Test Step 7.

Result: There was less than 100 K ohms of resistance between The signal wire at the affected sensor terminal and engine ground.

There is a short circuit in the wiring harness. Repair or replace the wiring harness.

If the problem is not resolved, proceed to Test Step 7.
 

7. Check the PWM Circuit for a Pin to Pin Short Circuit

A. Turn the main disconnect switch to the OFF position.

B. Disconnect the air/fuel pressure module.

C. Disconnect the J1 connector at the ECM.

D. Measure the resistance between the following locations for the sensor:

- The signal wire at the affected sensor and all ECM connector pins
 

Short Circuit
 

Result: There was more than 100 K ohms of resistance between the signal pin at the ECM and all other pins in the ECM connector.

Proceed to Test Step 8.

Result: There was less than 100 K ohms of resistance between the signal pin at the ECM and all other pins in the ECM connector.

There is a short circuit in the wiring harness. Repair or replace the wiring harness

If the problem is not resolved, proceed to Test Step 8.
 

8. Perform the Wiggle Test

Carefully following this procedure is the best way to identify the root cause of an intermittent problem.

A. Turn the main disconnect switch to the ON position.

B. Connect Cat ET.

C. Use Cat ET to perform the following test:

- "Wiggle Test"

D. Slowly wiggle the wiring and the connectors between the P2 connector and the sensor. Pay particular attention to the wiring near each connector. Be sure to wiggle all of the wiring. As you wiggle the wiring look for the following problems:

- Loose connectors or damaged connectors
- Moisture on the connectors or the wiring
- Damaged that is caused by excessive heat
- Damage that is caused by chafing
- Improper routing of wiring
- Damaged insulation
 

Test
 

Result: The wiring failed the Wiggle Test.

There is a problem with the wiring harness. Repair or replace the wiring harness.

Verify that the repair eliminated the problem.

Result: The wiring passed the Wiggle Test.

The problem may be intermittent. Inspect the wiring. Refer to Troubleshooting, "Electrical Connectors - Inspect" for additional information.

Repair: Perform the following procedure:

1 Turn the main disconnect switch to the OFF position.

2. Disconnect the connectors. Carefully inspect the terminals for proper installation.

3. Insert a pin into each socket. Verify that each socket grips the pin firmly. Repair any problems.

4. Connect all connectors.

Verify that the repair eliminated the problem.
 

If the procedure did not correct the issue, contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).

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