What it means
Same as P0737 with the output shorted to supply. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
How it works
The transmission control module (TCM) uses an engine-speed output circuit to receive or report engine-speed information used in transmission control. P0739 sets when that circuit reads high, which can happen if the signal wire is shorted to a supply voltage or a connector has a poor contact.
Common causes
Most likely first.
- Output line shorted to supply
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Record freeze-frame data and compare the scan tool's engine-speed signal with engine RPM and related transmission data to see when the high reading occurs.
- Inspect the engine-speed output wire and its connectors for chafing, water entry, corrosion, pushed-back pins, or contact with a power wire.
- With the circuit active, gently move the accessible harness while watching the scan-tool reading for a change that helps locate an intermittent short.
- Use the vehicle wiring diagram to check whether the signal wire is shorted to a power feed and inspect connector pin fit and continuity as specified by the manufacturer.
- If the wiring and connectors pass, test the relevant speed-signal source and TCM circuit according to the manufacturer's diagnostic procedure.
Common fixes
- Repair chafed or pinched wiring that is contacting a power source.
- Dry, clean, or repair a water-damaged or corroded connector and restore proper pin fit.
- Secure the harness away from rubbing points and power wiring.
- Repair or replace a faulty speed-signal source or TCM only after circuit testing confirms it.
Can I keep driving?
Avoid hard acceleration and long trips if shifts are harsh, delayed, or missing. If the transmission enters limp mode or slips, stop driving when safe; continued operation can worsen transmission damage.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.