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Electronic Control System Gas Plus Engines – FAULT CODE 421

Engine Oil Temperature High – Over Temperature Warning

Overview

CODE REASON EFFECT
Fault Code: 421
PID: P175
SPN: 175
FMI: 0/16
LAMP: Amber
SRT: 

High oil temperature – over temperature warning.

Progressive power derate increasing in severity from time of alert. If engine protection shutdown feature is enabled, engine will shut down 30 seconds after red stop lamp starts flashing.

Engine Oil Temperature Sensor Circuit
SMALL | MEDIUM | LARGE

Circuit Description

The electronic control module (ECM) uses this combination pressure/temperature sensor for engine protection purposes.

Component Location

The engine oil pressure/temperature sensor is located in the block, underneath the ECM.

Shop Talk

All temperature sensors:

  • The resistance of the sensor varies with temperature. The reading you observe should compare to the following table if the sensor is functioning properly.
Temperature (°C) Temperature [°F] Resistance (ohms)
0 32 30k to 36k
25 77 9k to 11k
50 122 3k to 4k
75 167 1350 to 1500
100 421 600 to 675

The engine protection shutdown for oil temperature is a customer feature and will only be enabled at the customer’s request. This sensor will deactivate or disable the fuel control valve if this feature is utilized by the OEM.

Cautions and Warnings

 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 3822917 – female Deutsch/AMP/Metri-Pack test lead.

Troubleshooting Steps

STEPS SPECIFICATIONS
STEP 1. Check the fault codes.  
  STEP 1A. Read the fault codes. Fault Code 421 active?
  STEP 1B. Verify engine oil temperature is high. Engine oil temperature high?
STEP 2. Check the engine oil pressure/temperature sensor.  
  STEP 2A. Inspect the engine harness and engine oil pressure/temperature sensor connector pins. Dirty or damaged pins?
  STEP 2B. Read the fault codes. Fault Code 421 active?
  STEP 2C. Check the resistance of the sensor. 300 to 90k ohms?
STEP 3. Clear the fault codes.  
  STEP 3A. Disable the fault code. Fault Code 421 inactive?
  STEP 3B. 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 INSITE™ electronic service tool.

Action

Read the fault codes.

Fault Code 421 active?
YES NO
No Repair No Repair

Guided Step 1B – Verify engine oil temperature is high.

Conditions

  • Turn keyswitch ON.

Action

  • Verify engine oil temperature by using the mechanical gauge.

Engine oil temperature high?
YES NO

Refer to the Lubricating Oil Temperature Above Specifications troubleshooting symptom chart in Section TS of the Troubleshooting and Repair Manual C Gas, C Gas Plus, and L Gas Plus Engines, Bulletin 3666206 or the Troubleshooting and Repair Manual B5.9G, B5.9LPG, B Gas Plus, and B LPG Plus Engines, Bulletin 3666164 .

 No Repair

Guided Step 2 – Check the engine oil pressure/temperature sensor.

Guided Step 2A – Inspect the engine harness and engine oil pressure/temperature sensor connector pins.

Conditions

  • Turn keyswitch OFF
  • Disconnect engine harness connector 1 from the ECM
  • Disconnect the engine harness from the engine oil pressure/temperature sensor.

Action

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

Dirty or damaged pins?
YES NO

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 019-205.
  • Replace the engine harness. Refer to Procedure 019-043.
  • Replace the sensor. Refer to Procedure 019-155.
 No Repair

Guided Step 2B – Read the fault codes.

Conditions

  • Connect all components
  • Turn keyswitch ON.

Action

  • Start the engine and let it idle for one minute.
  • Read the fault codes with INSITE™ electronic service tool.

Fault Code 421 active?
YES NO
No Repair No Repair

Guided Step 2C – Check the resistance of the sensor.

Conditions

  • Disconnect engine harness connector 1 from the ECM
  • Disconnect the engine oil pressure/temperature sensor from the engine harness.

Action

  • Measure the resistance from the engine oil temperature SIGNAL pin to the engine oil pressure/temperature RETURN pin in the engine oil pressure/temperature sensor.
SMALL | MEDIUM | LARGE

300 to 90k ohms?
YES NO
No Repair

Replace the sensor. Refer to Procedure 019-155.

Guided Step 3 – Clear the fault codes.

Guided Step 3A – Disable the fault code.

Conditions

  • Connect all components
  • Turn keyswitch ON.

Action

  • Start the engine and let it idle for one minute.
  • Verify that Fault Code 421 is inactive.

Fault Code 421 inactive
YES NO
No Repair

Troubleshooting procedures need to be repeated from the beginning.

Guided Step 3B – Clear the inactive fault codes.

Conditions

  • Connect all components
  • Turn keyswitch ON.

Action

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

All fault codes cleared?
YES NO
No Repair

Troubleshoot any remaining active fault codes.
Repair complete
Appropriate troubleshooting charts
Last Modified:  28-Sep-2004
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Published by Jack

Hello, I'm Jack, a diesel engine fan and a blogger. I write about how to fix and improve diesel engines, from cars to trucks to generators. I also review the newest models and innovations in the diesel market. If you are interested in learning more about diesel engines, check out my blog and leave your feedback.