This fault code 334 DTCs document explains the engine coolant temperature sensor diagnostic for a Cummins ECM-controlled engine. It covers the fault reason, likely causes, connector inspections, INSITE™ checks, ECM and harness response tests, and final fault clearing steps.
Official fault code 334 DTCs document details
| Brand | Cummins |
|---|---|
| Model coverage | ISB6.7 CM2150 (2007-09); document section also identifies FAULT CODE 334 (QSB3.3) |
| System/Group | DTCs; Engine Coolant Temperature Sensor |
| Publication no. | Not shown in extract |
| Year/Revision | Last Modified: 20-Jul-2010 |
| Pages | 11 |
| File size | 0.2 MB |
| Format | |
| Language | English |
Document table of contents
- Overview
- Circuit Description
- Component Location
- Shop Talk
- FAULT CODE 334 (QSB3.3)
- Engine Coolant Temperature – Data Erratic, Intermittent, or Incorrect
- Associated Procedures
- Troubleshooting Steps
- Guided Step 1 – Check for sensor circuit fault codes.
- Guided Step 2 – Check the engine coolant temperature sensor and circuit.
- Guided Step 3 – Check the ECM and engine harness.
- Guided Step 4 – Clear the fault code.
Applicable truck models
This file applies to Cummins ISB6.7 CM2150 (2007-09) diagnostic coverage in the DTCs group, with the extracted fault section naming FAULT CODE 334 (QSB3.3). The procedure is for an engine coolant temperature reading that is erratic, intermittent, or incorrect, where the ECM estimates coolant temperature because the coolant temperature value is not changing with engine operating conditions. The component location given is the thermostat housing, and the document directs users to Procedure 100-002 (Engine Diagrams) in Section F for a detailed component location view. For official manufacturer information, visit Cummins official website.
Who needs this fault code 334 DTCs manual
Mechanics, fleet technicians, and workshop owners need this manual when diagnosing an amber lamp condition with PID P110, SPN 110, and FMI 2. It is useful for checking Fault Codes 144 and 145, inspecting coolant temperature sensor connector pins, testing signal and return circuit response, and deciding when harness repair, sensor replacement, or ECM authorization is required.
The troubleshooting flow starts by checking active sensor circuit fault codes with the INSITE™ electronic service tool. It then moves through sensor connector inspection for loose connectors, corrosion, bent or broken pins, moisture, damaged seals, dirt, wire insulation damage, broken shells, or damaged locking tabs. Later steps isolate the engine harness and ECM connector, use jumper-wire checks between the engine coolant temperature SIGNAL pin and RETURN pin, and verify whether Fault Code 144 or Fault Code 145 becomes active after the required response time. The final procedure requires the coolant temperature to be near ambient air temperature before start-up, then the engine is operated until thermostat opening temperature so the diagnostic can see a coolant temperature change.
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