Damaged, chafed or corroded wiring in the engine speed output circuit (open circuit, short to earth or short to voltage); Poor connections at the TCM or engine control module plugs, including water ingress or bent or loose terminals; Faulty crankshaft position sensor or its wiring, giving the TCM a poor engine speed source; Low battery voltage or a poor earth or power supply to the TCM; Internal fault in the TCM (may be a mechatronic or integrated valve body unit on some models); Fault in the engine control module or another module that receives the engine speed signal; Outdated or faulty TCM software where a manufacturer bulletin identifies it as a known cause.

P0737

TCM Engine Speed Output Circuit.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
7: AreaTransmission
37: FaultThe specific fault in that area

What it means

P0737 is the generic code for a fault in the transmission control module (TCM) engine speed output circuit. The TCM sends an engine speed signal to other modules, and it has detected that the signal circuit is not behaving as expected, for example through an incorrect voltage or a fault in the circuit. How the fault is detected and which modules use the signal varies by manufacturer and model.

Symptoms

Malfunction indicator lamp or transmission warning lamp on
Rev counter erratic, reading zero or not working on some vehicles
Harsh, delayed or erratic gear changes
Transmission stuck in a fixed gear (limp mode)
Poor fuel economy or reduced performance
Other warning lamps or stored communication codes in related modules

Possible causes

Damaged, chafed or corroded wiring in the engine speed output circuit (open circuit, short to earth or short to voltage)likely
Poor connections at the TCM or engine control module plugs, including water ingress or bent or loose terminalslikely
Faulty crankshaft position sensor or its wiring, giving the TCM a poor engine speed sourcepossible
Low battery voltage or a poor earth or power supply to the TCMpossible
Internal fault in the TCM (may be a mechatronic or integrated valve body unit on some models)possible
Fault in the engine control module or another module that receives the engine speed signalrare
Outdated or faulty TCM software where a manufacturer bulletin identifies it as a known causerare

How to diagnose

Read all stored codes and freeze frame data, and note any engine, communication or crankshaft sensor codes that point to a related fault
Check the battery condition and charging voltage, as low voltage can set false circuit faults in the TCM
Inspect the wiring and connectors between the TCM and the engine control module for chafing, damage, corrosion, water and loose or pushed-back pins
Check the TCM power and earth supplies against the manufacturer wiring diagram
With the engine running, watch the live engine speed value in the TCM and compare it with the engine control module value and the rev counter
Test the engine speed signal circuit for continuity, short to earth and short to voltage with the connectors disconnected, following the model-specific procedure
Check the crankshaft position sensor and its wiring if engine speed data is missing or unstable
Check for manufacturer service bulletins or software updates relevant to the vehicle before considering the TCM faulty

How to fix

Repair or replace damaged wiring and terminals in the engine speed signal circuit
Clean, secure or replace corroded or loose connectors and fix any source of water ingress
Restore a sound battery, power supply and earth connection to the TCM
Replace a faulty crankshaft position sensor if it is found to be the source of the poor signal
Replace or repair the TCM, or the integrated unit, only once the wiring and supplies are proven good, and code or program it as the manufacturer requires
Apply a manufacturer software update where an outdated or faulty calibration is a known cause

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but gear changes may be harsh or the gearbox may go into limp mode, which can put extra strain on the transmission. Have it diagnosed soon, and avoid heavy loads or long journeys if shifting is poor.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.