Detailed Description of Error P0738
OBDII error code P0738 is a generic trouble code that indicates a problem with the Transmission Control Module (TCM) engine speed output circuit. The TCM is responsible for controlling the transmission''s gear shifts, torque converter engagement, and other functions. The engine speed output circuit is a critical component of the TCM, as it provides the module with the engine''s rotational speed, which is necessary for proper transmission operation.
When the TCM detects an engine speed output circuit voltage that is lower than expected, it will set code P0738. This code is typically accompanied by other transmission-related codes, such as P0700 or P0715. The low engine speed output circuit voltage can cause the transmission to malfunction, leading to symptoms such as erratic shifting, slipping, or failure to engage into gear.
Possible Causes of Error P0738
- Short circuit or open circuit in the engine speed output circuit wiring
- Corrosion or damage to the engine speed output circuit connector
- Faulty or malfunctioning engine speed sensor
- TCM malfunction or faulty programming
- Engine mechanical issues, such as low engine compression or worn engine bearings
- Wiring or connector issues between the engine speed sensor and the TCM
- Powertrain control module (PCM) malfunction
Possible Fixes for Error P0738
- Inspect the engine speed output circuit wiring and connectors for signs of damage or corrosion. Repair or replace as necessary.
- Check the engine speed sensor for proper operation and replace if faulty.
- Use a scan tool to monitor the engine speed output circuit voltage and verify that it is within the manufacturer''s specified range.
- Check the TCM for proper operation and reprogram or replace if necessary.
- Perform a thorough engine mechanical inspection to identify and address any underlying issues.
- Consult a professional mechanic or transmission specialist if the problem persists after attempting the above fixes.
