P0737 TCM Engine Speed Output Circuit Malfunction

The P0737 trouble code is an OBD-II diagnostic trouble code related to the Transmission Control Module (TCM) engine speed output circuit.

P0737 – TCM Engine Speed Output Circuit Malfunction

This code means that the TCM has detected a problem with the engine-speed output signal or circuit used by the transmission control system.

The transmission needs accurate engine-speed information to determine when and how to shift gears. Engine RPM information is also important for torque converter clutch control, transmission slip calculations and pressure management.

Depending on the vehicle, the engine-speed information may be generated from the crankshaft position sensor, calculated by the PCM, transmitted through a dedicated circuit or shared between the PCM and TCM over the vehicle's communication network.

P0737 is a relatively general code. Unlike P0738 (Circuit Low) and P0739 (Circuit High), it does not specifically identify the signal as too low or too high.

What Does P0737 Mean?

P0737 can be understood as:

P = Powertrain
0 = Generic OBD-II code
7 = Transmission-related system
3 = Transmission-specific code group
7 = Specific fault identifier

The important description is:

TCM Engine Speed Output Circuit Malfunction

The TCM has determined that the engine-speed output signal is not behaving as expected.

This does not necessarily mean that the engine-speed sensor itself is defective.

The problem could exist anywhere along the signal path.

For example:

Engine Speed Sensor → PCM → Communication Network → TCM

or, on another vehicle:

Engine Speed Signal → TCM

The exact architecture varies by manufacturer and transmission.

What Is the Engine Speed Signal?

Engine speed is the rotational speed of the engine, normally expressed in RPM.

The transmission control system needs this information because engine RPM is one of the key parameters used to control an automatic transmission.

The TCM may use engine-speed information to determine:

• Shift timing

• Gear selection

• Shift pressure

• Torque converter clutch operation

• Transmission slip

• Engine braking

• Protection strategies

If the signal becomes unreliable, the TCM may no longer be able to control the transmission correctly.

Does P0737 Mean the Engine RPM Is Wrong?

Not necessarily.

P0737 indicates a malfunction in the engine-speed output circuit or signal path.

The engine itself may be operating normally.

For example, the engine could actually be turning at 2,000 RPM while the TCM receives an incorrect, unstable or missing RPM signal.

This is why comparing actual engine RPM, PCM RPM and TCM RPM is an important diagnostic step.

Symptoms of P0737

Possible symptoms include:

• Check Engine Light

• Transmission warning light

• Harsh shifting

• Delayed shifting

• Incorrect shift timing

• Unexpected upshifts

• Unexpected downshifts

• Transmission stuck in one gear

• Limp mode

• Abnormal RPM readings

• Torque converter clutch problems

• Poor fuel economy

• Reduced acceleration

• Transmission slipping

• Erratic transmission behavior

Some vehicles may store P0737 while continuing to drive relatively normally.

What Does P0737 Feel Like While Driving?

Harsh gear changes

Incorrect engine-speed information can cause the TCM to command inappropriate shift timing or pressure.

Delayed shifting

The transmission may hesitate before changing gears.

Unexpected gear changes

The TCM may select a gear that does not match actual engine operating conditions.

Limp mode

The transmission may enter a failsafe strategy to protect itself.

RPM fluctuations

The displayed RPM or transmission behavior may not correspond correctly to vehicle speed and engine load.

Torque converter problems

Incorrect engine-speed information can affect TCC engagement and release.

Common Causes of P0737

Faulty engine-speed signal

The signal reaching the TCM may be missing, distorted or unstable.

Faulty crankshaft position sensor

On many vehicles, engine RPM is derived from the crankshaft position sensor.

Faulty camshaft position sensor

Some engine-control systems use camshaft information together with crankshaft data.

Damaged sensor wiring

Broken, chafed or shorted wiring can disrupt the RPM signal.

Poor electrical connection

Loose or corroded terminals can cause an intermittent or distorted signal.

Short to ground

A signal circuit shorted to ground may prevent a correct signal from reaching the control module.

Short to voltage

A signal circuit receiving unintended voltage can also produce an invalid signal.

Open circuit

A broken wire can cause the signal to disappear.

High resistance

Corrosion or damaged wiring can weaken the signal.

Damaged reluctor or tone wheel

The crankshaft position sensor relies on a trigger mechanism. Mechanical damage can produce an abnormal signal.

PCM problem

The PCM may incorrectly process or transmit engine-speed information.

CAN communication problem

On vehicles where RPM information is transmitted digitally, communication problems can prevent the TCM from receiving correct data.

Poor TCM ground

An inadequate ground can interfere with the TCM's ability to process signals correctly.

Poor PCM ground

A poor PCM ground can also affect engine-speed signal processing.

Low system voltage

Low or unstable electrical voltage can interfere with electronic modules.

TCM internal fault

A TCM internal circuit failure can cause P0737.

Is P0737 Serious?

P0737 can be serious because engine-speed information is important to transmission operation.

If the TCM cannot reliably determine engine speed, it may have difficulty controlling:

• Gear changes

• Shift pressure

• Torque converter lockup

• Transmission protection strategies

The vehicle may enter limp mode.

The seriousness depends on the actual symptoms and the root cause.

A damaged connector may be a simple repair, while a communication problem or control-module failure may require more extensive diagnosis.

Can You Drive With P0737?

If the vehicle is operating normally, a short drive to a repair facility may be possible.

However, continued driving should be avoided if you experience:

• Severe shifting

• Transmission slipping

• Limp mode

• Loss of gears

• Sudden unexpected downshifts

• Severe hesitation

• Engine stalling

Incorrect engine-speed information can result in incorrect transmission control.

P0737 vs. P0738

P0737 – TCM Engine Speed Output Circuit Malfunction

A general malfunction in the engine-speed output circuit.

P0738 – TCM Engine Speed Output Circuit Low

The TCM detects a low engine-speed output signal.

P0737 does not specifically identify a low signal condition.

P0737 vs. P0739

P0737 – TCM Engine Speed Output Circuit Malfunction

General engine-speed output circuit malfunction.

P0739 – TCM Engine Speed Output Circuit High

The TCM detects an engine-speed output signal higher than expected.

P0737 vs. P0725

P0725 – Engine Speed Input Circuit

Generally concerns the engine-speed information entering the transmission control system.

P0737 – TCM Engine Speed Output Circuit Malfunction

Concerns the TCM's engine-speed output signal/circuit.

The precise circuit architecture varies between vehicles, so the manufacturer's wiring diagram should always be consulted.

Where Does the Engine-Speed Signal Come From?

The source depends on the vehicle.

Common configurations include:

• Crankshaft position sensor

• Camshaft position sensor

• PCM-generated RPM information

• Dedicated engine-speed signal

• CAN communication between PCM and TCM

Modern vehicles frequently exchange engine-speed information digitally rather than using a simple dedicated wire.

How to Diagnose P0737

P0737 should be diagnosed systematically.

Replacing the TCM immediately is not recommended.

1. Scan all control modules

Use a professional diagnostic scanner to check:

• PCM

• TCM

• ABS

• Body control module

• Other networked modules

Look for additional codes related to:

• Crankshaft position

• Camshaft position

• Engine speed

• Transmission speed sensors

• CAN communication

• System voltage

Additional codes can provide important clues.

2. Check live engine RPM

Compare:

• Actual engine RPM

• Dashboard RPM

• PCM RPM

• TCM RPM

If these values disagree, determine where the discrepancy begins.

For example:

Actual RPM: 2,000

PCM RPM: 2,000

TCM RPM: 0

This would strongly suggest a problem in the communication path, TCM input or TCM processing rather than a simple mechanical engine-speed problem.

3. Check freeze-frame data

Review:

• Engine RPM

• Vehicle speed

• Engine load

• Transmission temperature

• Selected gear

• Battery voltage

• TCC status

This helps determine when the fault occurred.

4. Check battery and charging voltage

Inspect:

• Battery voltage

• Alternator output

• Battery terminals

• Engine grounds

• Chassis grounds

• PCM grounds

• TCM grounds

5. Inspect wiring

Look for:

• Broken wires

• Chafing

• Short circuits

• Melted insulation

• Pinched wiring

• Poor previous repairs

6. Inspect connectors

Check the relevant connectors for:

• Corrosion

• Bent pins

• Loose terminals

• Water intrusion

• Damaged seals

• Poor terminal tension

7. Test the crankshaft position sensor

If engine-speed information originates from the crankshaft sensor, verify:

• Power supply

• Ground

• Signal

• Connector

• Wiring

• Sensor installation

An oscilloscope can be particularly useful for examining the sensor waveform.

8. Check the reluctor/tone wheel

Inspect for:

• Damaged teeth

• Incorrect spacing

• Excessive runout

• Mechanical damage

• Incorrect sensor-to-reluctor clearance

A damaged trigger wheel can produce a faulty RPM signal even when the sensor itself is good.

9. Check the camshaft position sensor

If the vehicle uses camshaft data in calculating engine speed or synchronization, inspect its signal and wiring.

10. Compare PCM and TCM RPM

This is a critical diagnostic step.

If:

PCM RPM = Normal

but

TCM RPM = Incorrect

the technician should investigate the communication path and TCM.

If:

PCM RPM = Incorrect

and

TCM RPM = Incorrect

the problem is more likely to originate upstream, such as the crankshaft sensor, camshaft sensor, wiring or PCM.

11. Check CAN communication

If engine RPM is transmitted over the CAN network, inspect:

• CAN High

• CAN Low

• Network connections

• Module power

• Module grounds

• Communication errors

A CAN fault can cause apparently unrelated transmission codes.

12. Check the TCM output circuit

On vehicles using a dedicated output circuit, test:

• Voltage

• Frequency

• Continuity

• Resistance

• Short to ground

• Short to voltage

• Signal waveform

Use the manufacturer's specifications.

13. Check TCM power and ground

Perform voltage-drop testing on the TCM power and ground circuits.

A ground may look visually perfect but still have excessive resistance under load.

14. Test the TCM

If the engine-speed source, wiring, connectors, communication network, power and grounds are all verified, the TCM may be considered as a possible cause.

Can a Bad Crankshaft Position Sensor Cause P0737?

Yes, depending on the vehicle's design.

The crankshaft position sensor is commonly used to determine engine speed.

A weak, intermittent or missing signal can result in incorrect engine-speed information reaching the TCM.

However, P0737 does not prove that the crankshaft sensor is defective.

Can a Bad Camshaft Sensor Cause P0737?

Potentially.

Some systems use camshaft information as part of engine-speed and engine-position calculations.

Can a Bad TCM Cause P0737?

Yes.

An internal TCM circuit or processing problem can cause an engine-speed output malfunction.

However, the TCM should only be condemned after the external circuits have been tested.

Can a Bad PCM Cause P0737?

Yes, depending on the vehicle.

The PCM may calculate, process or transmit engine-speed information used by the TCM.

Can a CAN Bus Problem Cause P0737?

Yes.

If engine-speed information is transmitted through CAN communication, a network problem can cause missing or invalid RPM data.

Can Low Battery Voltage Cause P0737?

Yes, potentially.

Low system voltage can interfere with electronic modules and sensors.

The charging system and module grounds should be checked.

Can High Alternator Voltage Cause P0737?

Potentially.

Excessive charging voltage can cause abnormal electronic behavior and affect control modules.

Can P0737 Cause Transmission Problems?

Yes.

Incorrect engine-speed information can affect:

• Shift timing

• Gear selection

• Shift pressure

• TCC operation

• Transmission protection strategies

Can P0737 Cause Limp Mode?

Yes.

The TCM may activate failsafe operation if engine-speed information is unreliable.

Can P0737 Cause High RPM?

The code itself does not mean that engine RPM is high.

It indicates a malfunction involving the engine-speed output signal.

Actual engine RPM must be compared with the RPM information seen by the TCM.

Can P0737 Cause Low RPM?

Again, the code does not necessarily mean the engine is physically running at low RPM.

The problem is with the engine-speed information or output circuit.

Can P0737 Cause Poor Fuel Economy?

Yes, indirectly.

Incorrect shift timing or torque converter operation can reduce drivetrain efficiency.

Can P0737 Cause Harsh Shifting?

Yes.

The TCM depends on engine-speed information when controlling gear changes.

Common Diagnostic Mistakes With P0737

Replacing the TCM immediately

A sensor, connector, wiring or CAN problem can cause the code.

Replacing the crankshaft sensor without testing

The sensor may be good while the wiring or reluctor is damaged.

Assuming P0737 means the engine RPM is incorrect

The engine may be running normally while the TCM receives incorrect information.

Ignoring related codes

Crankshaft, camshaft and communication codes can reveal the actual source of the problem.

Checking only continuity

A circuit can have continuity and still suffer from high resistance or intermittent faults.

Ignoring module grounds

Poor grounds can create signal-processing problems.

Ignoring charging voltage

Abnormal system voltage can affect multiple modules.

Using the wrong wiring diagram

The engine-speed signal path is different from one vehicle to another.

What Is the Correct Repair for P0737?

The correct repair depends on the confirmed cause.

Possible repairs include:

• Repairing damaged wiring

• Repairing an open circuit

• Repairing a short to ground

• Repairing a short to voltage

• Replacing damaged connector terminals

• Cleaning connector corrosion

• Repairing PCM/TCM grounds

• Replacing a faulty crankshaft position sensor

• Replacing a faulty camshaft position sensor

• Repairing a damaged reluctor or tone wheel

• Repairing CAN communication wiring

• Correcting low or unstable system voltage

• Updating PCM software

• Updating TCM software

• Reprogramming the TCM

• Repairing the TCM output circuit

• Replacing the TCM if its failure is confirmed

• Repairing or replacing the PCM if its failure is confirmed

How to Test the Vehicle After Repair

After the repair, verify that engine-speed information remains accurate throughout the operating range.

Check that:

• Actual engine RPM is correct

• PCM RPM matches actual engine speed

• TCM RPM matches PCM RPM

• Engine-speed data remains stable

• CAN communication is normal

• Transmission shifts correctly

• Torque converter clutch operation is normal

• Limp mode does not activate

• No additional codes appear

• P0737 does not return

The vehicle should be road-tested at different engine speeds, vehicle speeds, gears and engine loads.

Frequently Asked Questions About P0737

What does P0737 mean?

P0737 means the TCM has detected a malfunction in the engine-speed output circuit.

Does P0737 mean the engine is running incorrectly?

Not necessarily. The engine can operate normally while the TCM receives incorrect engine-speed information.

Can a crankshaft position sensor cause P0737?

Yes, depending on the vehicle's system architecture.

Can a camshaft position sensor cause P0737?

Potentially.

Can wiring cause P0737?

Yes.

Can a short to ground cause P0737?

Yes.

Can a bad connector cause P0737?

Yes.

Can a CAN communication problem cause P0737?

Yes, on vehicles that transmit engine-speed information over the CAN network.

Can a bad TCM cause P0737?

Yes, but the external circuit should be tested first.

Can a bad PCM cause P0737?

Yes, depending on how the vehicle generates and transmits engine-speed information.

Can P0737 cause harsh shifting?

Yes.

Can P0737 cause limp mode?

Yes.

Can P0737 cause poor fuel economy?

Yes, indirectly.

Can P0737 damage the transmission?

Incorrect transmission control can increase stress and heat, so the underlying problem should be repaired promptly.

Can I drive with P0737?

If the vehicle operates normally, a short trip to a repair facility may be possible. If it enters limp mode, shifts violently or loses normal gear operation, continued driving should be avoided.

Does P0737 mean the transmission needs to be rebuilt?

No. P0737 is an engine-speed output/signal problem and does not automatically indicate internal transmission failure.

Final Thoughts on P0737

P0737 – TCM Engine Speed Output Circuit Malfunction indicates that the transmission control system has detected a problem with the engine-speed signal or output circuit.

Unlike P0738 and P0739, P0737 does not specifically state that the signal is too low or too high. It simply indicates that the signal is not operating within the expected conditions.

The most useful diagnostic approach is:

Scan All Modules → Check Live RPM → Compare Actual/PCM/TCM RPM → Check Battery Voltage → Inspect Wiring → Inspect Connectors → Test Crankshaft/Camshaft Signals → Check CAN Communication → Test TCM Circuit → Evaluate PCM/TCM

The fault can originate from a sensor, wiring, connector, trigger wheel, communication network, PCM or TCM.

Therefore, P0737 should not automatically be interpreted as a transmission failure. Finding where the engine-speed information becomes incorrect is the key to making an accurate and cost-effective repair.