The lambda sensor heater P1138 Fault Code P1138 diagnostic service manual is a technical reference published by PACCAR for the 2013 MX engine family equipped with EPA 2013 emissions control. This document provides comprehensive guidance on identifying, diagnosing, and resolving lambda sensor heater circuit faults that trigger diagnostic trouble code P1138 on PACCAR MX-series diesel engines.
Fault code P1138 is defined as “Lambda Sensor heater – Voltage too low or short circuit to ground on ECU D420 pin C46.” The code sets after one trip with the MIL active and requires three drive cycles to recover. This manual addresses the oxygen sensor heater control system, which maintains the lambda sensor at approximately 750°C [1382°F] during engine operation.
Document details and specifications — lambda sensor heater
| Brand | PACCAR |
| Model coverage | 2013 PACCAR MX Engines |
| System/Group | DTCs / MX Engines (EPA2013) |
| Publication no. | P1138 |
| Year/Revision | 2013 |
| Pages | 5 |
| File size | 0.5 MB |
| Format | |
| Language | English |
Table of contents
- Code number P1138 and fault code description
- Fault code information (trip count, recovery cycles, readiness group)
- Description of component(s) – lambda sensor function and air/fuel ratio measurement
- Sensor heater operation and heating control stages
- Effect on the system – smoke limit, NOx emissions, DPF regeneration
- Location of component(s)
- Diagnostic condition and set/reset conditions
- Electrical diagram(s) – wiring harness connectors D420 and F834
- Technical data – component check and circuit check procedures
- Possible causes – faulty wiring, connectors, and sensors
- Diagnostic Step-by-Step troubleshooting (Steps 1–5)
- Verification drive cycle procedure
Applies to these models
This lambda sensor heater P1138 manual applies to 2013 PACCAR MX-series diesel engines equipped with EPA 2013 emissions control systems. The document covers the oxygen sensor heater circuit connected to ECU D420 pin C46 and sensor connector F834. Technicians should refer to official PACCAR technical resources and PACCAR official website for current engine specifications and service bulletins.
Who needs this lambda sensor heater P1138 manual
Fleet mechanics and workshop owners servicing PACCAR MX diesel trucks need this sensor heater P1138 diagnostic guide to resolve P1138 faults efficiently. The step-by-step troubleshooting procedure guides technicians through electrical circuit testing, component verification, and harness inspection without causing damage to sensitive engine control systems.
The complete sensor heater P1138 fault code P1138 diagnostic service manual is available in the DiagTechPro manuals library. A free account is required to download the full 5-page PDF document and access additional PACCAR diagnostic resources.
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