P0720 on GMC vehicles
Transmission Output Speed Sensor Malfunction — what it means on a GMC, whether it's safe to drive, and the fixes by model and year.
P0720 on a GMC means transmission output speed sensor malfunction. Most vehicles stay drivable short-term, but diagnose it promptly. The most common cause is failed output shaft speed sensor element (typically $150–$500). Pick your GMC model below for its known failure patterns, recalls, and TSBs.
What does P0720 mean on a GMC?
P0720 is set when the transmission control module does not receive a valid signal from the output shaft speed sensor. The TCM uses this signal to compare actual transmission output to expected output for the selected gear and engine RPM — if the signal is missing or implausible, gear ratio calculations fail and the TCM cannot shift correctly. The vehicle typically drops into limp mode (stuck in a default gear, often 3rd or 4th) until the signal is restored.
P0720 is a standardized OBD-II code, so its definition is the same on every GMC. What differs by model and engine is which cause is most likely — pick your GMC model below for a diagnosis tuned to its known failure patterns, recalls, and TSBs.
Is it safe to drive a GMC with P0720?
In most cases a GMC stays drivable for short trips with P0720 active, but diagnose and repair it promptly. This is a high-severity code — ignoring it can lead to further damage or a failed emissions test. Exact tolerance depends on the model and engine.
What causes P0720 on a GMC?
| Cause | Likelihood | Estimated repair (USD) |
|---|---|---|
| Failed output shaft speed sensor element | Most common | $150–$500 |
| Damaged sensor connector or harness | Common | $80–$350 |
| Metal debris on the sensor tip (from internal transmission wear) — Cleaning the sensor face is a free first attempt. | Common | $100–$400 |
| Damaged tone ring or reluctor wheel inside the transmission | Occasional | $1,500–$4,500 |
| Transmission fluid contamination preventing the sensor from reading | Occasional | $200–$700 |
| Wiring fault between the sensor and the TCM | Occasional | $100–$500 |
| Failed TCM signal input (rare) | Rare | $500–$1,500 |
Repair costs are typical US ranges and vary by GMC model, model year, and labor rate. A diagnostic trouble code is a symptom, not a guaranteed failed part — confirm the root cause before replacing anything.
P0720 by GMC model
Select your GMC model and year for a P0720 diagnosis tuned to that vehicle's failure patterns, recalls, and TSBs.
GMC Sierra 1500
988 NHTSA owner complaints · 14 recalls on record across the years covered below.
Complaint and recall counts are NHTSA totals for the model years covered on this site, not counts specific to P0720.
P0720 on other makes
Other codes on GMC vehicles
P0720 on a GMC: frequently asked questions
What does diagnostic trouble code P0720 mean on a GMC?
P0720 is set when the transmission control module does not receive a valid signal from the output shaft speed sensor. The TCM uses this signal to compare actual transmission output to expected output for the selected gear and engine RPM — if the signal is missing or implausible, gear ratio calculations fail and the TCM cannot shift correctly. The vehicle typically drops into limp mode (stuck in a default gear, often 3rd or 4th) until the signal is restored. P0720 is a standardized OBD-II code, so the definition is the same on every GMC — which cause is most likely varies by model and engine.
What are the symptoms of P0720 on a GMC?
Check Engine Light is illuminated. Speedometer reads zero or fluctuates erratically. Transmission locked into a single gear (limp mode). Hard, harsh, or no shifts. Cruise control inoperative. Vehicle may shudder or hesitate at the moment of shift. Often paired with P0700 (transmission control malfunction)
What causes P0720 on a GMC?
Failed output shaft speed sensor element (most-common). Damaged sensor connector or harness (common). Metal debris on the sensor tip (from internal transmission wear) (common). Damaged tone ring or reluctor wheel inside the transmission (occasional). Transmission fluid contamination preventing the sensor from reading (occasional). Wiring fault between the sensor and the TCM (occasional). Failed TCM signal input (rare) (rare)
Is it safe to drive a GMC with P0720?
In most cases a GMC stays drivable for short trips with P0720 active, but it should be diagnosed and repaired promptly — this is a high-severity code. Ignoring it can lead to further damage or a failed emissions test. Exact tolerance depends on the model and engine.