1. What is P0720?

P0720 is a Diagnostic Trouble Code that indicates a Transmission Output Speed Sensor Circuit Malfunction. The output speed sensor monitors the rotational speed of the transmission’s output shaft, providing critical data to the TCM (Transmission Control Module) for proper shift timing and torque converter lockup. P0720 triggers when the TCM detects irregular voltage, no signal, or implausible data from this sensor circuit.

Why It Matters for Chevrolet Silverado 1500

For Silverado owners—especially those with 6-speed, 8-speed, or 10-speed automatic transmissions—accurate output speed data is vital for smooth shifting and towing performance. A malfunctioning sensor can cause harsh shifts, delayed engagement, or limp mode activation (limiting speed to protect the transmission). Towing with P0720 increases risk of overheating and premature wear. Addressing it promptly prevents costly transmission damage.

2. Common Causes in Chevrolet Silverado 1500

P0720 often stems from issues affecting the transmission output speed sensor or its circuit. Common Silverado-specific causes include:

• Failed output speed sensor — Internal coil or magnet degradation, common in high-mileage trucks with 100,000+ miles.
• Wiring or connector faults — Corroded pins, damaged insulation, or loose connections (vulnerable near the transmission case and underbody).
• Low transmission fluid — Insufficient fluid can cause sensor signal interference or damage.
• Damaged tone ring — Cracked or worn tone ring (the reluctor wheel the sensor reads) producing erratic signals.
• TCM software issues — Outdated calibration misinterpreting valid sensor data (addressed in GM TSB 21-NA-231 for 2019–2022 models).

3. Key Symptoms in Chevrolet Silverado 1500

Owners typically notice one or more of these P0720-related symptoms:

• Check Engine Light illuminated with P0720 (often paired with P0700, TCM malfunction code)
• Harsh or delayed shifts, especially when accelerating from a stop
• Torque converter not locking up, causing increased fuel consumption
• Speedometer inaccuracy or intermittent operation
• UR1000 live data showing no or erratic output speed readings
• Limp mode activation with limited speed and fixed gear

4. Silverado 1500 Models Prone to P0720

While P0720 can occur across model years, certain Silverado 1500 variants show higher incidence due to sensor location and transmission design:

• 2014–2019 Silverado 1500 with 6L80/6L90 transmissions — Sensor prone to fluid contamination.
• 2017–2023 Silverado 1500 with 8L90 8-speed transmissions — Tone ring wear in high-torque applications.
• High-mileage (120,000+ miles) Silverados — General sensor and wiring degradation.
• Towing-focused models with heavy payload usage — Increased transmission stress accelerates wear.

GM TSB 21-NA-231 addresses P0720 in 2019–2021 Silverados, recommending TCM reflash and sensor inspection for specific VIN ranges.

5. Diagnostic Steps (Silverado 1500 Focus) with UR1000

Use UR1000 to test the output speed sensor circuit and identify whether the fault is sensor, wiring, or mechanical:

Case Example: A 2018 Silverado 1500 with 6L80 transmission showed P0720 and harsh shifts. UR1000 live data showed intermittent output speed drops. Resistance test was normal, but physical inspection found a corroded connector. Cleaning the connector and applying dielectric grease resolved P0720 and restored smooth shifting.

6. Fixes & Execution for Chevrolet Silverado 1500

Fix depends on identified root cause. UR1000’s tests help avoid unnecessary sensor replacement—25% of P0720 cases are wiring or fluid issues:

• Replace output speed sensor — If circuit tests fail, install OEM-equivalent (GM part #24227578 or equivalent). Located on transmission case, accessible from under vehicle.
• Repair wiring/connectors — Splice damaged wires with heat-shrink connectors; clean corrosion with contact cleaner and apply dielectric grease.
• Top off or replace transmission fluid — Ensure proper level and condition (use Dexron VI for most Silverado transmissions).
• Replace tone ring — If damaged, requires transmission removal in most cases (common in 8L90-equipped models with towing history).
• TCM reflash — Update software per GM TSB 21-NA-231 for 2019–2022 models with calibration-related issues.

Silverado-Specific Workflow

1. Always check transmission fluid level first—low fluid is a common and easily fixed cause of P0720 in Silverados.
2. For 2014–2018 models, inspect the sensor O-ring during replacement—leaking fluid contaminates sensors and causes premature failure.
3. After repairs, use UR1000 to verify output speed consistency during a 20-minute test drive, including highway speeds for torque converter lockup.

7. Repair Costs & Safety Tips for Silverado 1500

Critical Safety Precautions

• Disconnect the negative battery terminal before working on sensors or wiring to prevent electrical shorts.
• Use jack stands when accessing under-vehicle components—never rely solely on a jack.
• Allow transmission to cool before servicing to avoid burns from hot components.
• After repairs, test drive in a safe area to confirm proper shifting before normal operation.

8. Preventive Maintenance for Silverado 1500 P0720

Reduce P0720 risk with these steps:

• Change transmission fluid every 60,000 miles (45,000 if towing) to prevent sensor contamination.
• Inspect sensor wiring and connectors during fluid services—look for corrosion or damage.
• Check transmission fluid level monthly, especially in high-mileage trucks.
• Use UR1000 to monitor output speed sensor data quarterly, especially before towing season.
• Avoid aggressive driving habits that increase transmission stress and sensor wear.

9. Frequently Asked Questions

10. Summary

P0720 (Output Speed Sensor Circuit Malfunction) is a critical issue in Chevrolet Silverado 1500 models, affecting transmission shifting and performance. Using the UR1000 diagnostic tool—with its live data monitoring, circuit testing, and data logging—allows accurate diagnosis of whether the issue stems from a faulty sensor, wiring fault, fluid issue, or tone ring wear. Most cases resolve with sensor replacement, wiring repairs, or fluid service. Addressing P0720 promptly ensures smooth operation, prevents transmission damage, and maintains towing capability—essential for Silverado owners.