P0791 OBD-II Trouble Code: Intermediate Shaft Speed Sensor “A” Circuit

Our certified mechanics come to you · 12-month, 12,000-mile warranty

SCHEDULE P0791 DIAGNOSTIC Get a fair and transparent estimate upfront
Red-stars EXCELLENT RATING ON

Cost of diagnosing the P0791 code

P0791 is a diagnostic trouble code (DTC) for "Intermediate Shaft Speed Sensor “A” Circuit". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic for $70.00. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $30.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
Ford$70.00$30.00
Toyota$70.00$30.00
BMW$70.00$30.00
SCHEDULE P0791 DIAGNOSTIC Get a fair and transparent estimate upfront

Check Engine Light

P0791 code definition

The P0791 trouble code detects an issue with the intermediate shaft speed sensor circuit

What the P0791 code means

The P0791 code is a generic OBD-II trouble code that notes an issue with the transmission intermediate shaft speed sensor circuit, which relays shaft speed data to the powertrain control module (PCM). In general, the intermediate shaft speed should slowly increase until the shift point, but if the PCM notes that the output speed is not slowly increasing, then shift strategy cannot be determined, and the P0791 code will be stored. Additionally, if the PCM receives no signal, or an erratic signal from the shaft speed sensor, the code will also be detected.

What causes the P0791 code?

Potential causes for the P0791 trouble code include:

  • Malfunctioning intermediate shaft speed sensor
  • Malfunctioning input speed sensor
  • Malfunctioning output speed sensor
  • Defective shift solenoids
  • Dirty transmission fluid
  • Malfunctioning engine temperature sensors, or possibly other drivability sensors
  • Defective or damaged electrical components, such as wires and connectors
  • In very rare cases, a malfunctioning PCM

What are the symptoms of the P0791 code?

The P0791 code will usually be joined by the Check Engine Light illuminating on the instrument panel. The car will likely experience transmission issues, such as an inability to shift, or very harsh shifting. There may also be engine performance issues, including constant stalling or throttle hesitation, frequent engine misfires, and diminished fuel efficiency. It is also common for the speedometer to fail, or act erratically. In rare cases, the vehicle may have no drivability issues.

How does a mechanic diagnose the P0791 code?

The P0791 code will be diagnosed with the assistance of a standard OBD-II trouble code scanner. A reputable technician will use the scanner to assess the freeze frame data and gather information about the P0791 code. The mechanic will also check for the presence of any additional trouble codes, as codes should always be addressed in the order in which they appear on the scanner. The mechanic will then reset the codes and restart the vehicle, to see if the trouble code returns. If it does not, it should be assumed that there is an intermittent issue, or that the code was triggered erroneously.

If the trouble code does return, then the technician should start with a visual inspection of all of the system’s electrical components. Any damaged wires or connectors should be replaced. If it is noticed that the electrical components have been damaged by the failure of another component in the vehicle, then that should be addressed immediately. The transmission fluid should then be checked, to make sure it is clean and at a sufficient level.

The mechanic will then check the intermediate shaft speed sensor’s reference voltage and ground signals, and use a digital volt/ohmmeter to look for continuity in the circuits. Any circuits that do not meet the manufacturer’s specifications will require replacement. Following this, the input and output sensors can be inspected, along with the shift solenoids. If no issues have been found, an oscilloscope can be used to gather information from the transmission intermediate shaft speed sensor.

After any component is replaced, the mechanic should once again reset the codes, restart the vehicle, and check to see if the code returns. By doing this, the technician will know as soon as the problem has been fixed.

Common mistakes when diagnosing the P0791 code

The most common mistake that is made when diagnosing the P0791 code comes from failing to properly follow the OBD-II trouble code diagnosis protocol. It is imperative that the protocol be adhered to at all times, to assure that all inspections, diagnoses, and repairs are successful and efficient. It is very common for the vehicle speed sensor to be erroneously replaced.

How serious is the P0791 code?

In most cases, a vehicle with the P0791 code cannot be driven, or will experience serious performance problems when it is driven. Continuing to drive the vehicle in this condition can be dangerous, and can cause further damage. Because of this, the P0791 code should be addressed as soon as it is detected, even if the car is drivable.

What repairs can fix the P0791 code?

Some repairs for the P0791 trouble code include:

Additional comments for consideration regarding the P0791 code

It is very rare for the PCM to be defective, and it should not be considered the problem unless all other potential issues have been checked. If the PCM does need to be replaced, it will also need to be reprogrammed.

Need help with a P0791 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

trouble codes
Check Engine Light
P0791

Fast and easy Check Engine Light is on Inspection service at your home or office.

SCHEDULE P0791 DIAGNOSTIC
Get a fair and transparent estimate upfront

Recent Check Engine Light is on Inspection reviews

Excellent Rating


YourMechanic Check Engine Light is on Inspection Service

Average Rating

4.5/5

Number of Reviews

3,484

Rating Summary
3,176
153
40
23
92
3,176
153
40
23
92

Richard

10 years of experience
415 reviews
Richard
10 years of experience
This is the second time I’ve had Richard work on my car. He always does an outstanding job and is quick, knowledgeable and professional. Highly recommended!!
2012 DODGE CHALLENGER - CHECK ENGINE LIGHT IS ON - LAS VEGAS, NEVADA

Michael

13 years of experience
372 reviews
Michael
13 years of experience
Mike was an absolute professional when he arrived. He walked me thru the whole process of my repairs and also made good recommendations for preventive issues. His mechanical knowledge and good customer services was a breath of air and greatly appreciated :-)
2007 CHEVROLET AVALANCHE - CHECK ENGINE LIGHT IS ON INSPECTION - MARIETTA, GEORGIA

Rodrigo

10 years of experience
85 reviews
Rodrigo
10 years of experience
Rodrigo was exactly on time, very professional and friendly. He assessed my car, let me know the exact problem when a previous mechanic from a shop in my area was unable to. I felt he was very honest and sincere letting me know the level of urgency that I deal with the issue. Absolutely no pressure. I will absolutely use Rodrigo the next time I need anything to do with my car and will tell everyone about him. This is such a great service, I will never go to another mechanic again. It is so convenient. I couldn’t be happier. :)
2013 SMART FORTWO - CHECK ENGINE LIGHT IS ON - LAS VEGAS, NEVADA

Ricardo

8 years of experience
223 reviews
Ricardo
8 years of experience
Great service and was very helpful on what maintenance my vehicle needed and what to expect in the future. Would definitely recommend to anyone and will.
2004 MITSUBISHI LANCER - CHECK ENGINE LIGHT IS ON - LOS ANGELES, CALIFORNIA

More related articles

How to Get a Louisiana Driver's Permit
s licensing program. The first step in this program is to obtain...
Veteran and Military Driver Laws and Benefits in New Mexico
The state of New Mexico offers a number of benefits and perks for those Americans who have either served in an Armed Forces branch...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...

Related questions

Q: Check engine Light on and medium consume increased fast

Hello, According to the numbers you have provided, the engine is consuming much more fuel than it is supposed to. You also mention that this began only after your Check Engine Light came on. From your description, it appears that...

Q: Q: Check Engine light; catalytic converter

When a catalytic converter begins to fail, the computer will give a reading of the code P0420 and/or code P0430 which pertains to catalyst efficiency. The catalytic converter is, in a way, like a metal filter that traps toxic gases...

Q: Check Engine Light came on gave me a O2 sensor code. A week later the car broke down and won't start. It now has catalytic converter code.

It is helpful if you include the codes numbers. There are numerous O2 sensor and catalytic converter codes. There are two O2 sensors on your car. One is monitors the fuel ratio and the PCM (powertrain control module) uses it...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1-800-701-6230 · hi@yourmechanic.com