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Electronic Control System Gas Plus Engines – FAULT CODE 234 – L Gas Plus

Engine Speed High – Critical

Overview

CODE REASON EFFECT
Fault Code: 234
PID: 190
SPN: 190
FMI: 0/0
LAMP: Red
SRT: 

Engine Speed High – Critical. Engine Speed High – Data Valid but Above Normal Operational Range – Most Severe Level. Engine speed signal indicates engine speed above engine protection limit,

Spark and fuel disabled until engine speed falls below the overspeed limit.

Camshaft and Crankshaft Speed and Position Sensors Circuit
SMALL | MEDIUM | LARGE

Circuit Description

The crankshaft (primary) engine speed/position sensor and the camshaft (back-up) engine speed/position sensor provide engine speed and position information to the electronic control module (ECM) through the engine harness.

Component Location

The crankshaft speed sensor is located on the intake side of the engine near the number 6 cylinder at the crankshaft centerline. The camshaft speed/position sensor is located in the gear housing, above the air compressor.

Shop Talk

Possible causes of this fault code include:

  • External fuel sources drawn into the intake air passage
  • Reverse powering (motoring) of the engine
  • Tampering of the engine speed/position sensors.

Make sure the correct operation conditions are followed when operating the engine as described in the operation and maintenance manual. To check for valid overspeed, check the fault code snapshot information for the speed reached. This fault will activate at 2800 rpm on the L Gas Plus engine.

Cautions and Warnings

 CAUTION 

If the engine speed stays above 3500 rpm, the engine must be shut off immediately or engine damage will occur.
 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 lead when taking a
measurement:
Part Number 3823996 – female Weather-Pack test lead.

Troubleshooting Steps

STEPS SPECIFICATIONS
STEP 1. Identify the reason for the overspeed.  
  STEP 1A. Check for proper operating conditions. Motoring downhill?
  STEP 1B. Check for an alternate fuel source Alternate fuel source?
  STEP 1C. Check the engine rpm with INSITE™ electronic service tool. Correct rpm reading?
  STEP 1D. Inspect the engine harness and engine sensor connector pins. Dirty or damaged pins?
  STEP 1E. Check for an active fault code at low engine rpm. Inactive fault code at low rpm?
  STEP 1F. Test the vehicle. Fault Code 234 inactive?
STEP 2. Clear the fault codes.  
  STEP 2A. Disable the fault code. Fault Code 234 inactive?
  STEP 2B. Clear the inactive fault codes. All fault codes cleared?

Guided Step 1 – Identify the reason for the overspeed

Guided Step 1A – Check for proper operating conditions.

Conditions

  • Turn keyswitch OFF

Action

  • Check if the engine was motoring downhill when the fault was logged.

Motoring downhill?
YES NO

Check for engine damage.

  • Electronics are OK.
  • Check the base engine for damage due to overspeed condition.
 No Repair

Guided Step 1B – Check for an alternate fuel source.

Conditions

  • Turn keyswitch OFF.

Action

  • Check if the driver reported a fuel-controlled event where the engine rapidly accelerated without accelerator pedal being depressed.
SMALL | MEDIUM | LARGE

Alternate fuel source?
YES NO

Locate any alternate fuel sources, such as operating the engine near flammable vapors, etc.

 No Repair

Guided Step 1C – Check the engine rpm with INSITE™ electronic service tool.

Conditions

  • Turn keyswitch ON
  • Engine is running
  • Connect INSITE™ electronic service tool.

Action

  • Compare the engine speed reading on INSITE™ electronic service tool to a mechanical tachometer or the dash tachometer.
SMALL | MEDIUM | LARGE

Correct rpm reading?
YES NO
No Repair

Inspect the crankshaft engine speed sensor and camshaft engine position sensor as outlined in Fault code 115 and Fault Code 121.

Fault Codes 689 and 778

Guided Step 1D – Inspect the engine harness and engine speed sensor connector pins.

Conditions

  • Turn keyswitch OFF
  • Disconnect the engine harness from the engine speed sensors.

Action

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

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

Dirty or damaged pins?
YES NO

A defective connection has been detected in the sensor or harness connector.

Repair the damaged connector pins. Repair or replace the engine harness, 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.
No Repair

Guided Step 1E – Check for an inactive fault code at low engine rpm.

Conditions

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

Action

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

Inactive fault code at low rpm?
YES NO
No Repair

Replace the ECM. Call for pre-authorization.

Refer to Procedure 019-031.

Guided Step 1F – Test the vehicle.

Conditions

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

Action

  • Use INSITE™ electronic service tool to read the fault codes.
SMALL | MEDIUM | LARGE

Fault Code 234 inactive?
YES NO
No Repair

Troubleshooting procedures need to be repeated from the beginning.

Guided Step 2 – Clear the fault codes.

Guided Step 2A – Disable the fault code.

Conditions

  • Connect all components
  • Connect INSITE™ electronic service tool.

Action

  • Start the engine and let it idle for one minute.
  • Use INSITE™ electronic service tool to verify that Fault Code 234 is inactive.

Fault Code 234 inactive?
YES NO
No Repair No Repair

Guided Step 2B – Clear the inactive fault codes.

Conditions

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

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:  17-Aug-2004
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