The vehicle’s computer decides when to shift gears, based on the load from the engine and the speed of the vehicle. One of the ways that the ECU gathers this data, is with sensors like the intermediate shaft speed sensor. Also referred to as the ISS sensor, this little device measures how fast the intermediate shaft is spinning inside the transmission. If the ECU notices a problem with the circuit that the intermediate shaft speed sensor labeled C operates on, a P2749 DTC will be triggered.
How Serious is the Code?
Given the fact that the ECU needs the ISS sensor to know when to change gears, a P2749 diagnostic trouble code is rather important. Not only will you experience a number of drivability issues, your vehicle safety could be affected if the engine stalls, or you experience a serious hesitation when trying to merge in traffic.
Symptoms of a P2749 include:
- Delayed, harsh or erratic shifts
- Transmission not able to shift gears
- Engine misfire
- Hesitation when accelerating
- Engine stalling
- Limp Mode
- Speedometer failure
- Failed intermediate shaft speed sensor
- Failed transmission input speed sensor
- Failed transmission output speed sensor
- Broken, loose or corroded connectors
- Wiring damage or shorts
- Valve body or pressure related issues
- Failed solenoid
- Failed engine temperature sensor
How to Diagnose the Code?
One of the first things that should be done when trying to diagnose a P2749 OBDII trouble code, is to make sure the transmission fluid is clean and at the proper level. The wiring and connectors on the transmission wiring harness should also be checked, to see if there or any shorted/broken wires or corroded connectors. Manufacturer TSB’s should also be researched see if there are any known causes or solutions to this transmission problem. If no problems have been found at this point, then the intermediate shaft speed sensor/ISS sensor will need to be tested directly. Along with possibly the output speed sensor, input speed sensor, engine temperature sensor and shift solenoids.
What Repairs Will Fix P2749?
- Replace intermediate shaft speed sensor
- Replace output speed sensor
- Replace input speed sensor
- Repair or replace damaged wiring and/or connectors
- Replace the engine temperature sensor
- Change transmission fluid and filter
- Flush transmission fluid
- Fix transmission fluid leaks
- Reprogram ECU/TCM
- P2745 – Intermediate Shaft Speed Sensor B Circ
- P2746 – Intermediate Shaft Speed Sensor B Circ Range/Performance
- P2747 – Intermediate Shaft Speed Sensor B Circ No Signal
- P2748 – Intermediate Shaft Speed Sensor B Circ Intermittent
- P2750 – Intermediate Shaft Speed Sensor C Circ Range/Performance
- P2751 – Intermediate Shaft Speed Sensor C Circ No Signal
- P2752 – Intermediate Shaft Speed Sensor C Circ Intermittent