P0731: Gear 1 Incorrect Ratio
Quick answer
P0731 is the standardised OBD-II code for gear 1 Incorrect Ratio. This narrows the general incorrect gear ratio fault down to first gear specifically not achieving its correct ratio when commanded. The most likely cause is low or degraded transmission fluid, not the most expensive one. Keep any driving short and light until it is repaired.
Severity 3 of 4. Short trips only.
Fix now · Short trips only
| Code | P0731 |
|---|---|
| Standard name | Gear 1 Incorrect Ratio |
| System | Transmission |
| Subsystem | Transmission gear ratio |
| Sets the | Comprehensive component monitor |
| Severity | Fix now (3 of 4) |
| Safe to drive | Short trips only |
| Tool needed | Scanner with live data |
| Cause | How often | What to check |
|---|---|---|
| Low or degraded transmission fluid | Most likely | The most common and cheapest cause to check first. |
| Worn first gear clutch pack | Common | Worn friction material cannot hold first gear ratio correctly. |
| Sticking shift solenoid for first gear | Worth checking | A solenoid that does not fully move affects that specific gear. |
| Valve body wear | Less common | Worn passages in the valve body can affect fluid delivery to that gear circuit. |
| General internal transmission wear | Uncommon | Least likely to be the first cause found, but possible with high mileage. |
TOPDON TopScan Lite OBD2 Scanner, Bidirectional Scan Tool, 8 Resets & AI
Adds live sensor streams and freeze frame, which is what turns a code into a diagnosis rather than a guess.
Coverage varies by tool and by model year, so check a specific tool against a specific vehicle before buying.
What is the engine computer reporting with P0731?
This narrows the general incorrect gear ratio fault down to first gear specifically not achieving its correct ratio when commanded.
The code sits in the transmission gear ratio area and is reported by the comprehensive component monitor. It names the circuit or the condition where the computer saw a reading outside its expected range. It does not name a failed part, and several genuinely different faults set this same code, which is the whole reason the causes below are ordered rather than listed.
What people usually notice
- Harsh or slipping engagement from a stop
- Engine revs without the vehicle accelerating as expected
- Delayed movement after shifting into drive
- Transmission warning light on
What is actually behind P0731?
The causes below are ordered by how often they turn out to be the answer, cheapest and most common first. That order matters more than the list itself: the expensive component named in the code text is very rarely the first thing to replace, and working down from the top is what stops a transmission gear ratio fault becoming an expensive guess.
Low or degraded transmission fluid is the one to rule out before anything else. The most common and cheapest cause to check first.
How do you diagnose P0731?
Start with freeze frame. Check the calculated ratio in first gear at the time the code set. That snapshot is taken at the instant the code set, and it is the single most useful piece of evidence you have, which is also why clearing the code before reading it is such a costly habit.
This code is diagnosed by watching values change rather than by reading the number again, so the tool has to stream live data and hold freeze frame. Live data on commanded versus calculated ratio in first gear specifically confirms the extent of the slip.
The order worth working in
- 1. Low or degraded transmission fluid: The most common and cheapest cause to check first.
- 2. Worn first gear clutch pack: Worn friction material cannot hold first gear ratio correctly.
- 3. Sticking shift solenoid for first gear: A solenoid that does not fully move affects that specific gear.
- 4. Valve body wear: Worn passages in the valve body can affect fluid delivery to that gear circuit.
- 5. General internal transmission wear: Least likely to be the first cause found, but possible with high mileage.
Can you keep driving with P0731?
Slipping in first gear is most noticeable from a stop, and continuing to drive on it accelerates wear on that gear clutch pack.
This is a severity 3 of 4 code, which means continuing to drive normally risks damage that costs considerably more than the repair in front of you. Treat the lamp as an instruction rather than a notification.
What does it cost to ignore P0731?
Continuing to drive with a slipping first gear accelerates wear that can spread to other gears over time.
There is also the diagnostic cost of waiting. Freeze frame data, pending code history and the readiness monitor state all describe the fault as it was when it set, and all of it is lost the moment somebody clears the code to make the lamp go out.
Tools that can diagnose P0731
Adds live sensor streams and freeze frame, which is what turns a code into a diagnosis rather than a guess.
- LJPXHHU
OBD2 Bluetooth Scanner Car Code Reader for iOS, Android and Windows
- wireless
$13.98 Check pricePrices change often - Veepeak
Veepeak Mini Bluetooth OBD2 Scanner Code Reader for Android (NOT for iOS)
- wireless
$14.99 Check pricePrices change often - MOCATEC
WiFi ELM327 OBD2 Adapter WiFi ELM 327 OBD Scanner for Universal 12V Vehicle
- wireless
$15.95 Check pricePrices change often - UMEIJA
OBD2 Scanner Diagnostic Tool, Car Scanner for iOS & Android, Bluetooth 5.4
- wireless
$29.99 Check pricePrices change often
Common questions
What does code P0731 mean?
P0731 is the generic OBD-II code for gear 1 Incorrect Ratio. This narrows the general incorrect gear ratio fault down to first gear specifically not achieving its correct ratio when commanded. It is a standardised definition, so it means the same thing on every manufacturer, although the fault behind it differs from car to car.
Can I drive with P0731?
Slipping in first gear is most noticeable from a stop, and continuing to drive on it accelerates wear on that gear clutch pack. On the severity scale this sits at 3 of 4, described as fix now. Whatever the code, a check engine light that starts flashing changes the answer immediately: that means an active misfire and the correct response is to reduce load and stop driving.
What is the most common cause of P0731?
Low or degraded transmission fluid is the cause worth ruling out first. The most common and cheapest cause to check first. Work down the ordered list rather than replacing the component named in the code text, because that component is the expensive answer and it is rarely the right one.
Will P0731 clear itself?
If the underlying fault genuinely goes away, the computer turns the lamp off after the monitor passes on a number of consecutive drive cycles, and the code moves to history before ageing out. A code that clears and returns is not fixed, it is intermittent. Clearing it manually erases the freeze frame data and resets every readiness monitor to incomplete.
What scanner do I need for P0731?
This code is diagnosed by watching values change rather than by reading the number again, so the tool has to stream live data and hold freeze frame. Live data on commanded versus calculated ratio in first gear specifically confirms the extent of the slip. Vehicle coverage still varies by tool and by model year, so check a specific tool against a specific vehicle rather than assuming a capability tier guarantees access.