P0736 – Reverse -incorrect ratio
Last Updated 2017-08-02
Automobile Repair Shop Owner
|Code||Fault Location||Probable Cause|
|P0736|| Reverse -incorrect ratio |
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|Wiring, TR sensor/switch, shift solenoids, transmission mechanical fault|
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Table of Contents
- What Does Code P0736 Mean?
- What are the common causes of code P0736 ?
- What are the symptoms of code P0736 ?
- How do you troubleshoot code P0736 ?
- Codes Related to P0736
- Get Help with P0736
What Does Code P0736 Mean?
SPECIAL NOTES: Non-professional mechanics should note that code P0736 – “Reverse -incorrect ratio” is generally not repairable on a DIY basis. Diagnosing and repairing this code requires the use of advanced diagnostic equipment that may include specialized transmission simulators, as well as advanced knowledge of automatic transmissions in general and expert- level knowledge of the affected application in particular.
For these reasons, the information provided here is intended for general informational purposes only, and should NOT be used in ANY diagnostic procedure for this code on ANY application without making proper reference to the repair manual for the affected application. Even so, non-professional mechanics are limited to a few basic diagnostic steps that may or may not resolve the problem. If the information provided here does not resolve the problem, do NOT attempt further repairs, but refer the vehicle to the dealer or a specialist transmission repairer for professional diagnosis and repair. END OF SPECIAL NOTES.
OBD II fault code P0736 is a generic code that is defined as “Reverse -incorrect ratio”, and is set when the PCM/TCM (Powertrain Control Module/Transmission Control Module) detects a problem while shifting into reverse gear, or while the vehicle is in motion with reverse gear selected. Note however that this code does not refer to a gear ratio as such, since most automotive applications have only one reverse gear ratio. This code refers to a transmission’s inability to select reverse gear, a transmissions’ inability to maintain the reverse gear selection, or to a situation where the transmission’s actual speed does not agree with the transmission’s desired or expected speed while reverse gear is selected.
While the shift pattern in the forward gears are accomplished/managed by computer controlled shift solenoids, reverse gear is typically purely hydraulically operated in the sense that the reverse gear hydraulic circuit is either pressurized, or not. Moreover, the act of selecting reverse gear is not computer controlled- the driver has to select/deselect reverse gear manually via the gear selector.
Therefore, the diagnostic procedures that might resolve a shifting issue in a forward gear do not apply to reverse gear. Additionally, transmission design specifics and code setting parameters vary greatly between manufacturers which means, that in practice, the diagnostic and repair procedures for this code depend entirely on the specific transmission that is fitted to the application. Nonetheless, when the PCM/TCM detects a problem with reverse gear selection, it will set code P0736, and illuminate a warning light.
What are the common causes of code P0736 ?
Some common causes of code P0736 could include the following-
- Dirty, contaminated, or degraded transmission fluid
- Low transmission fluid level
- Mechanical failure of transmission components, including but not limited to the pressure pump
- Internal pressure losses
- Clogged fluid passages
Failed or failing PCM/TCM. Note that control module failure is rare and the fault must be sought elsewhere before any control module is replaced
What are the symptoms of code P0736 ?
Some common symptoms of code P0736 could include the following-
- Stored trouble code and an illuminated warning light
- Reverse gear engagement may be delayed, or reverse gear may not engage at all
- Depending on the application, varying degrees of transmission slippage may be present
How do you troubleshoot code P0736 ?
NOTE: A dedicated transmission fluid pressure gauge may assist in diagnosing this code.
Record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault e diagnosed later on.
NOTE: If additional transmission related codes are present, note the order in which they were stored. Begin the repair by resolving all additional codes in the order in which they were stored, since doing this may very well resolve P0736 as well. Note however that this is not guaranteed, but it is possible for code P0736 to set as the result of one or more other codes setting.
If no other codes are present and the transmission is fitted with a dipstick, inspect the fluid level as well as the fluid’s condition. Top off the fluid level as required, but note that transmission fluid can only be lost through fluid leaks, so be sure to repair all leaks before returning the vehicle to service.
If the fluid id dark in color, has a “burnt” odor, or has a thick, tarry consistency, the fluid id degraded and it must be replaced.
WARNING: Be aware that transmissions with “life-time” fills are best left to professional personnel. Do NOT attempt to drain and refill such a transmission, since the average non-professional mechanic has no reliable way of determining if such a transmission is over-, or under filled. Note that both conditions can cause catastrophic transmission failure.
If the transmission fluid is serviceable and up to the mark, refer to the manual to locate the various pressure-testing points on the transmission, and particularly the point where the reverse gear pressure is to be tested. Since how well, or otherwise, reverse gear works depends on the available pressure in the hydraulic system, testing the system pressure is one of the few avenues of investigation open to non-professional mechanics.
NOTE: Testing transmission fluid pressure usually involves more than merely screwing a pressure gauge into the transmission. In most cases, the transmission has to be at a predefined temperature, and it has to rotate at a specified speed. Determine the correct procedure to follow before attempting to test any pressures at any point on the transmission. Note that failure to do this may result in transmission failure, or personal injury, or sometimes both.
Only attempt this step if the manual provides detailed information on the procedure. If it does, follow the direction exactly to avoid mistakes and possible misdiagnoses, and be sure to follow all recommended safety procedures to the letter to avoid serious personal injury.
The object of this step is to determine whether or not the pressure pump in the transmission is developing enough pressure for the transmission to work properly. Thus, be sure to obtain the most accurate and reliable test result possible to avoid replacing expensive transmission components unnecessarily.
Compare the obtained test pressure with the value stated in the manual. If the tested pressure is lower than the specified value, suspect a defective pressure pump, a clogged transmission fluid filter, or worn/damaged/broken transmission components that cause internal pressure losses.
If the test pressure agrees with the pressure stated in the manual, but the fault persists, suspect either internal blockages or restrictions in one or more fluid passages in the transmission, a defective selector mechanism, or mechanical failure of one or more transmission components.
If the tested pressure exceeds the specified value by any percentage, suspect one or more defective internal pressure relief valves or mechanisms.
It is NOT recommended that non-professional mechanics proceed with the diagnostic/repair procedure beyond determining that the fluid pressure in the transmission is either normal, or not. From this point on, a proper diagnosis requires removal and disassembly of the transmission, a procedure that is almost certainly beyond the skills and capabilities of the average DIY mechanic. At this point the better option is to refer the vehicle to the dealer or a specialist transmission repairer for professional diagnosis and repair.
Codes Related to P0736
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