P0791: Intermediate Shaft Speed Sensor A Circuit Malfunction
The P0791 code indicates a problem with the intermediate shaft speed sensor 'A' circuit. This sensor monitors the rotational speed of the intermediate shaft within the transmission. The Powertrain Control Module (PCM) uses this data to determine shift timing and torque converter lockup. When the signal is missing or out of range, the PCM sets this code. Common causes include a faulty sensor, damaged wiring, or internal transmission issues.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Harsh or erratic shifting
- Transmission slipping or delayed engagement
- Reduced fuel economy
2. Most Common Causes
- Faulty or worn intermediate shaft speed sensor 'A'
- Damaged, corroded, or loose sensor wiring
- Short to ground or voltage in the sensor circuit
- Moisture, corrosion, or bent pins in the sensor connector
- Internal failure of the transmission control module (TCM)
- Mechanical issue with the intermediate shaft or damaged reluctor ring
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Inspect transmission fluid level and condition.
Step 3: Visually check sensor wiring and connector for damage.
Step 4: Test sensor resistance and voltage with a multimeter.
Step 5: Compare sensor signal to manufacturer specifications.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with P0791 can cause transmission damage due to improper shifting or slipping.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, including parts and labor. Sensor replacement is usually $50-$150, plus diagnostic fees.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.