P0733

Gear 3 Incorrect ratio

P0733 is a generic OBD-II powertrain diagnostic trouble code: Gear 3 Incorrect ratio. It is logged by the engine control unit when the trans monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0733
Group
Powertrain
System
Trans
Severity
high
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What P0733 means

P0733 is a powertrain DTC indicating the transmission control module (TCM) has detected that the actual gear ratio in third gear differs from the expected calibrated value. Third gear is a critical cruising gear on most automatics — typically carrying a ratio near 1.0–1.5:1 — and is engaged heavily during highway on-ramps and sustained moderate-speed driving. The TCM continuously divides the input shaft speed by the output shaft speed and compares the result to its internal gear-ratio table; a deviation that persists beyond the programmed tolerance threshold causes the fault to be logged and the MIL to turn on.

As with the related codes P0731 and P0732, degraded or insufficient transmission fluid is the most common starting point: low fluid means the 3rd-gear clutch pack cannot fully apply, leading to slip that the TCM records as a ratio error. A faulty or stuck 3rd-gear shift solenoid — which directs hydraulic fluid to the clutch apply circuit — is the next most common cause. Mechanical wear of the third-gear friction discs or the steel reaction plates produces the same symptom once the material has worn thin enough to slip under the torque load of highway driving.

Electronic faults can mimic mechanical ones: a defective input speed sensor (ISS) or output speed sensor (OSS), corroded connectors, or a broken wire in the speed-sensor circuit can cause the TCM to compute a false ratio. CAN-bus communication errors between the TCM and other control modules, or an internally failing TCM, are less common but should not be excluded. A thorough, step-by-step diagnosis starting with fluid condition, moving to sensor validation and solenoid testing, and only then progressing to hydraulic pressure checks and internal inspection is the most cost-effective approach to resolving P0733 correctly.

Common causes

Most-frequently reported root causes when P0733 is logged.

  • 1
    Low or degraded transmission fluid reducing 3rd-gear clutch apply pressure
  • 2
    Faulty or stuck 3rd-gear shift solenoid
  • 3
    Worn or burnt third-gear clutch pack friction discs
  • 4
    Defective input shaft speed sensor or output/vehicle speed sensor
  • 5
    Damaged or corroded speed-sensor wiring and connectors
  • 6
    Valve body wear or restricted hydraulic passages for the 3rd-gear circuit
  • 7
    Failing transmission pump with insufficient line pressure
  • 8
    Torque converter clutch slipping during 3rd-gear operation
  • 9
    TCM software corruption or outdated calibration
  • 10
    Internal TCM hardware failure

Symptoms drivers notice

Check engine / MIL light illuminated
Transmission slipping or RPM flare in third gear without matching vehicle speed increase
Harsh, jerky or delayed shift into third gear
Vehicle enters limp-home mode, often locked in 2nd or 3rd gear
Reduced fuel economy during highway or mixed driving
Hesitation or stumble during mid-range acceleration
Burnt smell from transmission or discoloured / foamy fluid
Intermittent loss of third gear under heavy throttle

How to diagnose P0733

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and retrieve all stored DTCs; record freeze-frame data (engine RPM, vehicle speed, throttle position, gear state) captured at the moment P0733 was set
  2. 2
    Check transmission fluid level and condition — inspect colour, smell and clarity; perform a fluid and filter service if the fluid is burnt, dark or contaminated
  3. 3
    Visually inspect the wiring harness and connectors at the input speed sensor, output speed sensor, 3rd-gear shift solenoid and TCM for corrosion, chafing or broken pins
  4. 4
    Use scan-tool live data to monitor input shaft speed and output shaft speed simultaneously during a warm road test; calculate the ratio in each gear and confirm the deviation specifically occurs in 3rd gear
  5. 5
    Test the 3rd-gear shift solenoid with a multimeter (resistance) and scan-tool bi-directional control; compare readings to manufacturer specification and replace if faulty
  6. 6
    Perform a transmission line pressure test at the 3rd-gear circuit test port; low pressure indicates pump wear, valve body fault or blocked passages
  7. 7
    Check for TCM software updates or calibration bulletins and re-flash the TCM if applicable
  8. 8
    If all electrical and hydraulic tests pass, remove the transmission pan for valve body and clutch pack inspection; a full transmission teardown may be required if clutch material is severely worn

Related powertrain codes

Frequently asked questions

Is P0733 safe to ignore for a while?

No. Continued driving with a slipping 3rd-gear clutch pack accelerates friction material wear and generates heat that degrades fluid and other components. What may start as a solenoid or fluid issue can become a full clutch rebuild if neglected.

Can P0733 be caused by a TCM software bug rather than a physical transmission fault?

Yes. Corrupted or outdated TCM calibration tables can cause the module to misinterpret valid speed-sensor data as a ratio error. Check for manufacturer software updates before condemning any mechanical component.

Why does P0733 sometimes only appear under heavy acceleration?

Under light throttle the clutch pack may hold marginally despite wear or low pressure; heavy throttle greatly increases torque, overwhelming the reduced clamping force and causing the slip event that triggers the fault. Intermittent codes often point to borderline clutch wear or marginal hydraulic pressure.

What is the typical repair cost for P0733?

Costs vary widely by root cause: a fluid service may cost $80–$150, solenoid replacement $150–$400, wiring repair $100–$300, and a full clutch pack or transmission rebuild can reach $1,500–$3,500 or more depending on vehicle and labour rates.

If P0731, P0732 and P0733 are all set together, what does that indicate?

Multiple simultaneous gear-ratio codes strongly suggest a shared upstream cause — most commonly severely low fluid, a failing transmission pump, a bad input or output speed sensor, or a TCM fault — rather than independent failures on each gear's clutch pack. Diagnose the common elements first.

Disabling P0733 in software

RaceTune can permanently disable P0733 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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