|Code||Fault Location||Probable Cause|
|P0792|| Intermediate shaft speed sensor -range/performance problem |
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|Wiring, poor connection, intermediate shaft speed sensor, ECM/PCM!TCM|
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What Does Code P0792 Mean?
SPECIAL NOTES: Non-professional mechanics should take that note that diagnosing code P0792 – “Intermediate Shaft Speed Sensor “A” Circuit Range/Performance” could result in the loss of some transmission fluid. This is particularly important in cases where the transmission has a “life-time” fill, since it is not easy, and sometimes impossible to refill the transmission to the correct level on a DIY basis.
Therefore, if code P0792 appears on a transmission with a “life-time” fill, the better option is to refer the vehicle to the dealer or a specialist transmission repair shop for professional diagnosis and repair. END OF SPECIAL NOTES.
OBD II fault code P0792 is a generic code that is defined as “Intermediate Shaft Speed Sensor “A” Circuit Range/Performance”, and is set when the PCM (Powertrain Control Module) or TCM (Transmission Control Module) detects an abnormal voltage in the Intermediate Shaft Speed Sensor. Note that this code only applies to applications with automatic transmissions.
As the name suggests, the intermediate shaft in an automatic transmission is located between the input drive and the final output shaft, and while its primary purpose is to transfer power from the input drive to the transmission internals, it also allows various parts of the transmission to rotate at different speeds to allow for smooth gear shifts.
To ensure smooth and efficient operation of the transmission, the PCM/TCM uses several speed sensors to continually monitor the speeds at which various transmission components rotate. Since the intermediate shaft plays a crucial role in power transmission, its rotational speed is closely monitored and compared with output data from other transmission speed sensors. Note that since the rotational speed of the intermediate shaft is dictated by the gear the transmission is in, the PCM/TCM expects this shaft to rotate within a predefined range of speeds for each gear.
Thus, should the PCM/TCM detect a signal from the intermediate shaft speed sensor that falls outside of the expected range for any reason, either the PCM or the TCM will set code P0792, and depending on the application, the control module(s) may also illuminate one or more warning lights. However, on many applications, the PCM/TCM will also use input data from other transmission and engine speed sensors to calculate a “back-up” or “fail-safe” hydraulic pressure to keep the transmission functional, although gear selection and engine speed may be severely limited.
The image below shows a typical transmission intermediate shaft speed sensor. Note that depending on the application, these sensors may have either two or three wires in their connectors.
What are the common causes of code P0792 ?
Some common causes of code P0792 could include the following-
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
- Defective intermediate shaft speed sensor
- In some cases, other defective engine and/or transmission speed sensors can cause this code to set. However, in these cases the defective sensor(s) will almost certainly be indicated by dedicated codes
- Low transmission fluid levels
- Dirty, contaminated, or degraded transmission fluid
- 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 P0792 ?
Some common symptoms of code P0792 could include the following-
- Stored trouble code, and one or more illuminated warning lights
- Gear shifts may be harsh, erratic, or unpredictable
- Engine speed may fluctuate
- On some applications, the transmission may enter a fail-safe or limp mode
How do you troubleshoot code P0792 ?
NOTE: If the transmission is fitted with a dipstick, check the fluid level (and the condition of the transmission fluid) as a first step in the diagnostic/repair procedure. Adjust the fluid level as required, or replace the fluid and the internal filter as per the instructions in the manual if the fluid is dark in color, has a “burnt” odor, or has a thick, tarry consistency. Refer to the special notes at the top of this guide if the transmission has a “life-time” fill.
Assuming that the transmission fluid is serviceable, record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.
NOTE: If any other codes are present, refer to the manual to determine their relationship to P01792. Note however that codes that were stored after P0792 have likely set as a result of P0792, but in all cases where other codes precede P0792 these codes must be resolved before an attempt is made to diagnose P0792. Failure to do will almost certainly result in a misdiagnosis, wasted time, and the unnecessary replacement of parts and components.
Refer to the manual to locate the intermediate shaft speed sensor. Also determine the color-coding and function of each wire in the sensor connector/harness.
NOTE: Check that the connector is fastened securely, since it is common for this connector to be left undone after routine maintenance.
Perform a thorough visual inspection of all associated wiring. Look for damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors. Make repairs or replace wiring as required.
If no visible damage to wiring is found, prepare to perform reference voltage (where applicable), resistance, ground integrity, and continuity checks on all associated wiring, but be sure to disconnect the sensor from all relevant control modules to prevent damaging the controllers.
Compare all obtained reading with the values stated in the manual, and make repairs or replace wiring as required to ensure that all electrical values fall within the ranges specified by the manufacturer.
TIP: Since the intermediate shaft speed sensor is sometimes very difficult to access, perform the above-mentioned tests at the connector of the relevant control module by back-probing the connector pins. Note however that while this method tests both the circuit and the sensor at the same time, this way of doing things will not necessarily distinguish between a fault in the sensor and a fault in the circuit, and it may still be necessary to remove the sensor from the transmission for further testing or cleaning.
If Step 4 reveals an electrical issue, disconnect the sensor from its harness, and repeat Step 4 at the control module connector. If all electrical values check out, the sensor is defective. Conversely, if the sensor is disconnected and the fault persists, look for the problem in the wiring between the sensor connector and the control module. Make repairs as required, and repeat all tests to verify that the repair is successful.
If the speed sensor is shown to be defective, remove it from the transmission and inspect it for signs of mechanical damage, or the presence of excessive amounts of metal wear particles. Remove all wear particles, and check the sensors’ internal resistance to verify its overall condition. Replace the sensor with an OEM replacement if its resistance does not agree with the value specified in the manual.
Note however that if the sensor bears signs of mechanical damage on the part of the sensor that fits inside the transmission, there is nothing the average non-professional mechanic can do to fix the problem. Diagnoses of this type require removal and disassembly of the transmission, so in these cases, the better option is to refer the vehicle to the dealer or specialist transmission repair shop for professional assistance.
Clear all codes after all repairs are complete, and operate the vehicle normally to see if any codes return. In the unlikely event that any codes do return, suspect an intermittent fault that may require the use of advanced diagnostic equipment to diagnoses and repair.