01 Squealing Engine? Don't Panic! It Might Just Be Your Serpen… • 02 Understanding Clutches: Types, Advantages, and Disadvantage… • 03 P0056 – O2 Heater Circuit Fault (Bank 2 Sensor 2): Diagnosi… • 04 This Is Why Mixing Fuel Grades Or Pumping The Wrong Fuel De… • 05 Why Does Your Car Still Overheat After a Head Gasket Replac… • 06 What Parts Can a Car Engine Run Without? • 07 P0102 and P0103: Mass Air Flow (MAF) Sensor Circuit Low & H… • 08 The Sneaky Mechanical Piece That Increases Fuel Consumption… • 09 What Does It Mean When Your Car Says “Engine Power Reduced”? • 10 The Wankel Rotary Engine: Compact, Smooth, and Powerful •

DTC codes / P07xx · Transmission / P0737

P0737TCM Engine Speed Output Circuit

P0737 is set when the transmission control module (TCM) detects an abnormal condition on the engine speed output circuit, which is the signal path the TCM uses to report engine RPM to other modules or to verify its own output. The TCM monitors the voltage or signal integrity on this circuit and flags the code when the expected electrical behavior is not present.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaTransmission

Symptoms you may notice

  • Illumination of the malfunction indicator lamp (MIL) on the dashboard
  • Often no symptoms besides the warning light, with normal shift quality and drivability
  • Erratic or harsh shifting if the TCM loses engine speed data used for shift scheduling
  • Incorrect or missing tachometer reading on the instrument cluster
  • Transmission may enter limp mode or default to a fixed gear on some vehicles
  • Other modules may log communication or signal-loss codes related to engine speed

Common causes, most likely first

  1. Damaged, chafed, or open wiring in the engine speed output circuit between the TCM and the component it feeds
  2. Corroded or loose connector terminals at the TCM or at the receiving module
  3. Failed TCM output driver or internal circuit fault
  4. Faulty engine speed sensor or crank sensor providing an invalid input the TCM cannot output correctly
  5. Short to ground or short to voltage on the signal wire
  6. Poor ground connection shared by the TCM or the instrument cluster
  7. Aftermarket accessories or poor previous repairs tapping into the circuit

How to diagnose and fix it

  1. Scan all modules and record stored, pending, and permanent codes before clearing anything
  2. Inspect the TCM connectors and the engine speed output circuit for corrosion, loose pins, and chafed insulation
  3. Check continuity and resistance of the signal wire end to end, and test for shorts to ground and to voltage
  4. Verify the engine speed sensor input to the TCM is clean and consistent with a scan tool live data reading
  5. Confirm the receiving module or cluster is not the source of the fault by swapping or testing it where accessible
  6. If the circuit and inputs test good, follow the manufacturer's pinpoint test for the TCM output driver
  7. Replace or reprogram the TCM only after all wiring and input checks pass, then clear codes and verify the repair

What the engine speed output circuit really does

  • Many technicians replace the TCM first, but a chafed signal wire or corroded pin is far more common and costs far less to fix.
  • This code does not always mean the TCM has failed; a bad crank or engine speed sensor input can cause the TCM to output an invalid signal.
  • The engine speed output circuit often feeds the instrument cluster tachometer, so a dead tachometer alongside P0737 points to the wiring or cluster rather than the transmission itself.
  • A weak or shared ground can mimic a failed TCM output driver, so ground voltage drop testing should be part of every diagnosis.
  • Aftermarket remote starters, alarms, or stereo installs that tap into the tach or data wires are a commonly missed cause of this code.

Can I keep driving with P0737?

The vehicle is usually safe to drive short distances because the fault is electrical and often does not affect shifting, but avoid towing or aggressive driving until the circuit is repaired. If the transmission enters limp mode or shifts harshly, have it diagnosed promptly to prevent further damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage