P0738
TCM Engine Speed Output Circuit Low
Transmission
Generic OBD-II
High
What it means
P0738 means the transmission control module sees a low-voltage fault on the circuit it uses to output an engine-speed signal to other modules. That signal helps coordinate shifting and gauge readings, so a fault here typically shows up as erratic engine-speed readings and shift quirks rather than a no-start.
High
Can I keep driving? Usually yes, but you may see shifting quirks or odd tachometer/speed behavior; have it checked to avoid transmission problems.
Common symptoms
What you'll notice
- Check-engine light on
- Incorrect or erratic engine-speed readings
- Shifting issues or incorrect gear selection
- Harsh or delayed shifting
Common causes
Most likely first
- Short to ground or low-voltage fault in the engine-speed output wiringLikely
- Corroded or loose connectors in the output circuitCommon
- Fault in the module that receives the engine-speed signalCommon
- Faulty TCM (least likely)Less often
How to diagnose & fix
Work through it in order
- Scan and check the engine-speed signal the TCM is outputting.
- Inspect the output-circuit wiring and connectors for shorts to ground and corrosion.
- Check the receiving module and its connections.
- Verify the TCM power and ground connections.
- If wiring and connections are good, evaluate the TCM.
FAQ
Quick answers
Is it safe to drive with P0738?+
Usually yes for short trips, but the engine-speed signal other modules rely on is unreliable, so shifting and gauges may misbehave. Have it diagnosed soon.
Can I just clear P0738?+
You can, but a wiring or module fault sets it again; fix the output circuit rather than clearing it.
Related codes
Often seen with P0738
Read & clear P0738 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX