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Error Code P072B is defined as Stuck In Reverse. This is a generic but uncommon trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to present. This code normally appears to Audi, Ford, Mazda, Nissan, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.
Multiple modules and computers simultaneously monitor and adjust a variety of components and systems to ensure efficient and seamless operation every time a vehicle is driven. One of these components and systems include the A/T or Automatic Transmission.
Inside the A/T system are numerous components, moving parts, and systems that work with each other to ensure the right operation, such as ensuring the right gear according to the driver’s need. Another important component is the TCM (Transmission Control Module), which the main function is to monitor, adjust, and correlate different values, driver’s inputs, speed, etc., and shift the vehicle effectively for you. Considering the vast number of possibilities here, you would want to start with the basics.
When researching for error codes like this one, your vehicle is inoperable (as it’s stuck in reverse). Thus, it’s best to avoid trying to start the vehicle until the problem is fixed. Let’s say you’re stuck in the second gear while trying to get up to highway speed, and you may probably get it faster than 30m/h or 60km/h. With that said, the engine will be working extremely hard to keep up with the desired speed. This can cause a lot of stress in the engine and lead to serious damage in these vents.
The PCM (control module, also known as ECM or engine control module in other vehicle makes) will activate the Check Engine light and register the Error Code P072B when it determines an automatic transmission stuck in reverse.
Multiple symptoms of this include:
- Vehicle not moving
- Abnormal noise in the engine
- Low power
- Abnormal or limited vehicle speed
- Reduced throttle response
- ATF (Automatic Transmission Fluid) leak (red fluid under the vehicle)
Common causes for this error code include:
- Transmission hydraulics blockage
- Dirty, incorrect, or low ATF level
- A problem in shift solenoid
- TCM problem
- Open, shorted, chafing, or melting wires
- Broken tabs, corroded pins, melting connectors, etc.
How to Check
First, check the integrity of the ATF. Use a dipstick (if equipped) to check the level of the A/T, with the vehicle running and in the park position. This procedure may vary from one manufacturer to another. With that said, you can find more information on this in the service manual, which is sometimes in the dash or printed on the dipstick itself.
Make sure there’s clean fluid, free of any debris. If you don’t remember doing transmission service, then it’s best to have your transmission service accordingly. You would probably be surprised how dirty the ATF can affect the transmission’s functionality.
Note: To get accurate readings, make sure to check the ATF level on a flat surface. Also, use the fluid recommended by the manufacturer.
If you see leaks, and the fluid is low, then the fluid is probably going somewhere. You can check your driveway for any signs of oils or puddles.
Check the TCM for any signs of damage. If it’s in the transmission itself, or any other location where it may be subject to elements, then check for signs of water intrusion. This could lead to the problem, among other possible others. If there are signs of corrosion on the connectors or housing, then it’s a good sign of the problem
If everything is in good condition up to this point, depending on your OBS-II scanner’s capabilities, you can monitor the position of the gear and verify its functionality. With this, by merely driving the vehicle, it’s easy to say whether your transmission is shifting or not. Do you floor the gas pedal and it accelerates painfully slow? It’s probably stuck at higher gear (4, 5, 6, 7). Can you accelerate fast, yet the vehicle still can’t go as fast as you’d like? Then it’s probably stuck at lower gear (1, 2, or 3).
How to Fix
Depending on the diagnosis, common repairs for this code include:
- Use of the clean, recommended, and the correct level of ATF
- Repair or replacement of damaged shift solenoid
- Repair or replacement of open or shorted wiring
- Repair or replacement of damaged connector, or cleaning of corroded connector
In terms of severity, the Error Code P072B is actually considered moderately high. Meaning, it must be attended immediately. Sure, you may be able to drive the vehicle down the street, but it definitely needs immediate repair to prevent further damage. AT is an intricate type of transmission, and must be kept in good shape through proper maintenance.