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Electronic Control System Gas Plus Engines – FAULT CODE 123 – L Gas Plus

Mixer Inlet Pressure Sensor Circuit – Shorted Low

Overview

Mixer Inlet Pressure Sensor Circuit – Shorted Low

CODE REASON EFFECT
Fault Code: 123
PID: P102
SPN: 102
FMI: 4
LAMP: Amber
SRT: 

Mixer Inlet Pressure Sensor Circuit – voltage below normal or shorted to low source. Low signal voltage detected on the mixer inlet pressure signal pin at the ECM.

Engine power derate.

Mixer Inlet Pressure Sensor Circuit
SMALL | MEDIUM | LARGE

Circuit Description

The Mixer Inlet Pressure Sensor measures the inlet air pressure entering the fuel housing.

Component Location

The Mixer Inlet Pressure Sensor is located in the air inlet elbow.

Shop Talk

If the Mixer Inlet Pressure Sensor is disconnected, the engine can continue operating by using the accelerator plate position and the manifold pressure to estimate the mixer inlet pressure. Before performing any wiring checks, disconnect the sensor from the engine harness.

Cautions and Warnings

 CAUTION 

To reduce the possibility of damaging a new ECM, all other active fault codes must be investigated prior to replacing the ECM.
 CAUTION 

To reduce the possibility of pin and harness damage, use the following test leads when taking a measurement:
Part Number 3822758 – male Deutsch/AMP/Metri-Pack test lead
Part Number 3824775 – breakout cable.

Troubleshooting Steps

STEPS SPECIFICATIONS
STEP 1. Check the fault codes.  
  STEP 1A. Read the fault codes. Fault Code 227 active?
  STEP 1B. Check for an inactive fault code. Fault Code 122 inactive?
STEP 2. Check the Mixer Inlet Pressure Sensor and circuit.  
  STEP 2A. Inspect the Mixer Inlet Pressure Sensor connector pins. Dirty or damaged pins?
  STEP 2B. Check for circuit response. Fault Code 123 active and Fault Code 122 inactive?
  STEP 2C. Check the sensor supply voltage and return circuit. 4.5 VDC to 5.25 VDC?
  STEP 2D. Check the fault codes and verify sensor condition. Fault Code 122 active?
STEP 3. Check the ECM and engine harness.  
  STEP 3A. Inspect the ECM and engine harness connector pins. Dirty or damaged pins?
  STEP 3B. Check for an open circuit in the engine harness. Less than 10 ohms?
  STEP 3C. Check for a pin to pin short circuit in the engine harness. Less than 10 ohms?
  STEP 3D. Check for a pin to pin short circuit in the engine harness. More than 100k ohms?
  STEP 3E. Check for a pin short circuit to ground. More than 100k ohms?
  STEP 3F. Check for an inactive fault code. Fault Code 123 active?
STEP 4. Clear the fault codes.  
  STEP 4A. Disable the fault code. Fault Code 122 inactive?
  STEP 4B. Clear the inactive fault codes. All fault codes cleared?

Guided Step 1 – Check the fault codes.

Guided Step 1A – Read the fault codes.

Conditions

  • Turn keyswitch ON
  • Connect the INSITE™ electronic service tool.

Action

Use INSITE™ electronic service tool to read the fault codes.

Fault Code 187 active?
YES NO
No Repair No Repair
Fault Code 187.

Guided Step 1B – Check for inactive fault codes.

Conditions

  • Turn keyswitch ON
  • Connect the INSITE™ electronic service tool.

Action

  • Use INSITE™ electronic service tool to read the fault codes.

Fault Code 123 inactive?
YES NO
No Repair No Repair
Inactive or Intermittent Fault Code, Procedure 019-362

Guided Step 2 – Check the Mixer Inlet Pressure Sensor and circuit.

Guided Step 2A – Inspect the Mixer Inlet Pressure Sensor and connector pins.

Conditions

  • Turn keyswitch OFF
  • Disconnect the Mixer Inlet Pressure Sensor from the engine harness.

Action

  • Corroded pins
  • Bent or broken pins
  • Pushed back or expanded pins
  • Wire installation damaged
  • Moisture in or on the connector
  • Missing or damaged connector seals
  • Connector shell broken
  • Dirt or debris in or on the connector pins.

For general inspection techniques, refer to Component Connector and Pin Inspection, Procedure 019-361.

Dirty or damaged pins?
YES NO

Repair the damaged pins. Flush the dirt, debris, or moisture from the connector pins. Repair or replace the engine harness, or replace the sensor, whichever has the damaged pins.

  • Flush the dirt, debris, or moisture from the connector pins using electronic contact cleaner, Part Number 3824510.
  • Install the appropriate connector seal if it is damaged or missing.
  • Repair the engine harness. Refer to Procedure 019-202.
  • Replace the engine harness. Refer to Procedure 019-043.
  • Replace the sensor. Refer to Procedure 019-098.
 No Repair

Guided Step 2B – Check the sensor supply voltage and return circuit.

Conditions

  • Turn keyswitch OFF
  • Disconnect the Mixer Inlet Pressure Sensor from the engine harness
  • Turn keyswitch ON.

Action

  • Measure the voltage between the SUPPLY pin and the mixer inlet pressure RETURN pin at the Mixer Inlet Pressure Sensor connector of the engine harness.

Refer to the wiring diagram for connector pin identification.

4.5 VDC to 5.25 VDC?
YES NO
No Repair No Repair

Guided Step 2C – Check the circuit response.

Conditions

  • Turn keyswitch OFF
  • Disconnect the Mixer Inlet Pressure Sensor from the engine harness
  • Turn keyswitch ON
  • Connect the INSITE™ electronic service tool.

Action

  • Use INSITE™ electronic service tool to read the fault codes.

Fault Code 122 active and Fault Code 123 inactive?
YES NO
No Repair No Repair

Guided Step 2D – Check the fault codes and verify sensor condition.

Conditions

  • Turn keyswitch OFF
  • Disconnect the Mixer Inlet Pressure Sensor from the engine harness
  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

  • Use INSITE™ electronic service tool to read the fault codes.

Fault Code 123 active?
YES NO

Replace the Mixer Inlet Pressure Sensor. Refer to Procedure 019-098

No Repair

Guided Step 3 – Check the ECM and engine harness.

Guided Step 3A – Inspect the ECM and engine harness connector pins.

Conditions

  • Turn keyswitch OFF
  • Disconnect engine harness from the ECM.

Action

  • Corroded pins
  • Bent or broken pins
  • Pushed back or expanded pins
  • Wire insulation damaged
  • Moisture in or on the connector
  • Missing or damaged connector seals
  • Connector shell broken
  • Dirt or debris in or on the connector pins.

For general inspection techniques, refer to Component Connector and Pin Inspection, Procedure 019-361.

Dirty or damaged pins?
YES NO

Repair the damaged pins. Flush the dirt, debris, or moisture from the connector pins. Repair or replace the engine harness, or replace the ECM, whichever has the damaged pins.

  • Flush the dirt, debris, or moisture from the connector pins using electronic contact cleaner, Part Number 3824510.
  • Install the appropriate connector seal if it is damaged or missing.
  • Repair the engine harness. Refer to Procedure 019-204.
  • Replace the engine harness. Refer to Procedure 019-043.
  • Replace the ECM. Call for pre-authorization.
  • Refer to Procedure 019-031.
 No Repair

Guided Step 3B – Check for an open circuit in the engine harness.

Conditions

  • Turn keyswitch OFF
  • Disconnect the engine harness from the ECM
  • Disconnect the Mixer Inlet Pressure Sensor from the harness.

Action

  • Measure the resistance between the engine harness ECM connector SUPPLY pin and the engine harness Mixer Inlet Pressure Sensor connector SUPPLY pin.

Refer to the wiring diagram for connector pin identification.

For general resistance measurements refer to Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360.

Less than 10 ohms?
YES NO
No Repair

Repair or replace the engine harness.

  • Repair the engine harness. Refer to Procedure 019-204.
  • Replace the engine harness. Refer to Procedure 019-043.

Guided Step 3C – Check for an open circuit in the engine harness.

Conditions

  • Turn keyswitch OFF
  • Disconnect the engine harness from the ECM
  • Disconnect the Mixer Inlet Pressure Sensor from the harness.

Action

  • Measure the resistance between engine harness ECM connector SIGNAL pin and engine harness Mixer Inlet Pressure Sensor connector SIGNAL pin.

Refer to the wiring diagram for connector pin identification.

For general resistance measurements refer to Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360.
SMALL | MEDIUM | LARGE

Less than 10 ohms?
YES NO
No Repair

Repair or replace the engine harness.

  • Repair the engine harness. Refer to Procedure 019-204.
  • Replace the engine harness. Refer to Procedure 019-043.

Guided Step 3D – Check for a pin to pin short circuit in the engine harness.

Conditions

  • Turn keyswitch OFF
  • Disconnect the engine harness from the ECM
  • Disconnect the Mixer Inlet Pressure Sensor from the engine harness .

Action

  • Measure the resistance between the mixer inlet pressure SIGNAL pin in engine harness ECM connector 2 and all other pins in engine harness ECM connector 2.
  • Measure the resistance between the mixer inlet pressure SIGNAL pin in engine harness ECM connector 2 and all other pins in engine harness ECM connector 1.

Refer to the wiring diagram for connector pin identification.

For general resistance measurements refer to Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360.
SMALL | MEDIUM | LARGE

More than 100k ohms?
YES NO
No Repair

Repair or replace the engine harness.

  • Repair the engine harness. Refer to Procedure 019-204.
  • Replace the engine harness. Refer to Procedure 019-043.

Guided Step 3E – Check for a pin short circuit to ground.

Conditions

  • Turn keyswitch OFF
  • Disconnect the engine harness from the ECM
  • Disconnect the Mixer Inlet Pressure Sensor from the engine harness .

Action

  • Measure the resistance between the Mixer Inlet Pressure Sensor SIGNAL pin in engine harness ECM connector and ground.

Refer to the wiring diagram for connector pin identification.

For general resistance measurements refer to Resistance Measurements Using a Multimeter and Wiring Diagram, Procedure 019-360.

More than 100k ohms?
YES NO
No Repair

Repair or replace the engine harness.

  • Repair the engine harness. Refer to Procedure 019-204.
  • Replace the engine harness. Refer to Procedure 019-043.

Guided Step 3F – Check for an inactive fault code.

Conditions

  • Connect all components
  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

  • Use INSITE™ electronic service tool to read the fault codes.

Fault Code 123 active?
YES NO
No Repair
  • Call for pre-authorization.
  • Replace the ECM. Refer to Procedure 019-031.

Guided Step 4 – Clear the fault codes.

Guided Step 4A – Disable the fault code.

Conditions

  • Connect all components
  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

  • Start the engine and let it idle for one minute.
  • Use INSITE™ electronic service tool to verify the fault code is inactive.

Fault Code 123 inactive?
YES NO
No Repair No Repair

Guided Step 4B – Clear the inactive fault codes.

Conditions

  • Connect all components
  • Turn keyswitch ON
  • Connect INSITE™ electronic service tool.

Action

  • Use INSITE™ electronic service tool to erase the inactive fault codes.

All fault codes cleared?
YES NO
No Repair No Repair
Repair complete
Appropriate troubleshooting charts
Last Modified:  28-Sep-2004
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