P0720 on 2005-2015 Audi Q7: Output Speed Sensor Circuit Malfunction Causes and Fixes

What's Unique About the 2005-2015 Audi Q7

The first-generation Audi Q7 (Typ 4L) primarily used a 6-speed Aisin automatic transmission (TR-60SN, VW/Audi designation 09D), with later models getting an 8-speed ZF (TR-80SD, VW/Audi designation 0C8). For P0720, the key issue is often the Output Speed Sensor (G195) which, on the common 09D transmission, is located internally, bolted under the valve body. This makes replacement more involved than on vehicles with external sensors, as it requires draining the fluid and removing the transmission oil pan and sometimes the valve body to access it. A specific repair case on a Q7 noted that even with good sensor voltage, the fault could be traced to a faulty chip on the TCM itself, which is located under the front right seat and is highly susceptible to water damage from clogged sunroof drains.

Symptoms You May Notice

• Check Engine Light is on.
• Transmission warning light is on (often with a message like 'Gearbox Malfunction').
• Harsh, erratic, or delayed shifting.
• Transmission gets stuck in one gear (limp mode).
• Speedometer may work erratically or not at all.
• Decreased fuel efficiency.
• Cruise control may not function.
• PRNDS indicator on the dashboard may flash or not correctly show the selected gear.

Most Likely Causes

1. Faulty Transmission Output Speed Sensor (G195) 🔴 High Probability The sensor is an electronic component that can fail over time due to heat cycles and constant use within the transmission. It's the most common failure point for this code.
   How to confirm: A diagnostic scan tool can monitor the live data from the output speed sensor. If the reading is zero or erratic while the vehicle is moving, the sensor is likely faulty. The sensor's resistance can also be tested with a multimeter.
   Typical fix: Replace the output speed sensor. This requires draining the transmission fluid, removing the oil pan, and accessing the sensor, which is typically located under the valve body on the 09D transmission.
   Est. part cost: $50-$150
2. Damaged Wiring or Corroded Connectors 🟡 Medium Probability The internal transmission wiring harness is submerged in hot fluid, which can make it brittle over time. External wiring and the main connector on the transmission case are also prone to corrosion from road salt and moisture, which can cause intermittent signals and trigger the code.
   How to confirm: Visually inspect the wiring harness inside the transmission pan for any signs of brittleness, breaks, or burnt sections. Check the external connector at the transmission and the TCM for corrosion or loose pins. A user on a forum reported cleaning corroded plugs on the transmission loom fixed the issue.
   Typical fix: Repair the damaged section of the wire or replace the internal transmission wiring harness (OEM P/N 09D927363G or 09D927363F for the 09D transmission).
   Est. part cost: $100-$300
3. Low or Contaminated Transmission Fluid ⚪ Low Probability Fluid can become contaminated with metal shavings from normal wear. These metallic particles can stick to the magnetic tip of the speed sensor, disrupting its ability to get a clean reading. The 'lifetime' fluid can break down at high mileage, leading to shifting issues.
   How to confirm: Check the level and condition of the transmission fluid. If the fluid is dark, burnt-smelling, or contains visible metal particles, it is contaminated. Note that these transmissions do not have a dipstick and require a specific procedure using a scan tool to monitor temperature to check the fluid level correctly.
   Typical fix: Perform a transmission fluid and filter change. If significant metal is present, further diagnosis of the transmission's internal condition is needed.
   Est. part cost: $200-$400

Rare But Worth Checking

• Faulty Transmission Control Module (TCM): While less common, the TCM can fail internally. One documented case for a Q7 with P0720 and P0715 pointed to a failed chip on the TCM circuit board which was replaced to solve the problem. The TCM is located under the front right seat and can be susceptible to damage from water ingress into the cabin, a common Q7 issue due to clogged panoramic sunroof drains or AC drain tubes.
• Failed Valve Body: The valve body directs hydraulic pressure. While not a direct cause of the P0720 electrical code, severe mechanical issues or clogged solenoids within the valve body can sometimes lead to erratic transmission behavior that might be misdiagnosed.

Diagnosis Steps

1. Scan the vehicle's TCM for trouble codes. Confirm P0720 is present and note any other codes.
2. Use a scan tool with live data capability (like VCDS) to monitor the Transmission Output Speed Sensor signal while driving. The reading should increase smoothly with vehicle speed.
3. If the signal is absent or erratic, the next step is to inspect the transmission fluid level and condition. Note: This may require a professional as there is no dipstick and level must be checked at a specific temperature.
4. Inspect the passenger-side floor and under-seat area for any signs of moisture or water damage, as this can damage the TCM.
5. If the fluid is okay, inspect the external wiring and connectors between the transmission and the TCM for any visible damage or corrosion. Pay close attention to the main 14-pin connector on the transmission.
6. If external wiring is good, the transmission oil pan must be removed.
7. Visually inspect the internal wiring harness leading to the output speed sensor for damage, brittleness, or signs of overheating.
8. Test the sensor itself. Disconnect it and measure its internal resistance with a multimeter, comparing it to the manufacturer's specification. If the sensor and wiring test good, the fault may lie with the Transmission Control Module (TCM).

Parts You'll Likely Need

• Transmission Output Speed Sensor (OEM #09D927321B) — This is the most common component to fail, causing the P0720 code. This part number is for the 6-speed Aisin 09D transmission.
  Trusted brands: Bosch, VEMO, Genuine VW/Audi
  OEM price range: $100-$180
  Aftermarket price range: $40-$90
• Transmission Fluid (OEM #G055025A2) — The fluid must be drained to access the sensor and should be replaced with the correct specification fluid (e.g., ATF Type T-IV) during the repair.
  Trusted brands: Liqui Moly Top Tec 1200, Febi Bilstein 29934, Genuine VW/Audi
  OEM price range: $25-$40 per liter
  Aftermarket price range: $15-$25 per liter
• Transmission Oil Pan Gasket (OEM #09D321371) — The gasket must be replaced anytime the transmission oil pan is removed to prevent leaks.
  Trusted brands: Victor Reinz, Elring, Genuine VW/Audi
  OEM price range: $40-$70
  Aftermarket price range: $20-$40
• Internal Transmission Wiring Harness (OEM #09D927363G) — If the internal wiring is found to be brittle or damaged, it must be replaced. This harness connects the valve body solenoids and sensors to the external connector.
  Trusted brands: Genuine VW/Audi
  OEM price range: $250-$350
  Aftermarket price range: $150-$220

Related Codes That Often Appear With This One

• P0715 — This code relates to the Input/Turbine Speed Sensor (G182). Since the input and output sensors often share a wiring harness and power/ground circuits, a fault in one can sometimes trigger a code for the other. A documented repair case showed both codes appearing together and being traced to a faulty TCM.
• P0730 — Incorrect Gear Ratio. This code is often a direct result of the P0720 fault. If the TCM doesn't know the output speed, it cannot verify if the selected gear ratio is correct, leading to this code.

Platform-Specific Known Issues

• TCM Water Damage from Sunroof Drains: A very common issue on the first-generation Q7 is water leaking into the cabin from clogged panoramic sunroof drains. The front drains can get blocked with debris, causing water to overflow the drain channel and run down the A-pillar, soaking the passenger-side footwell carpet and foam. The Transmission Control Module (TCM) is located under this carpet, making it extremely vulnerable to water damage, which can cause a host of transmission codes, including P0720.
• Corroded External Transmission Connectors: A user on the Ross-Tech forums with a 2011 Q7 experienced flashing PRNDS lights and limp mode. They traced the issue to corrosion in multiple transmission loom plugs, including the main 14-pin connector. Cleaning the corrosion resolved the issue, highlighting the vulnerability of the external wiring to environmental factors.

Mechanic-Grade Diagnostic Values

• VCDS Live Data - Transmission Output Speed (G195) — expected: Should show 0 km/h when stopped and increase smoothly and correlate with the speedometer while driving.. Failure: A reading of 0 while the vehicle is moving, or an erratic/jumping reading, points to a fault in the sensor or its circuit.
• Output Speed Sensor (G195) Resistance — expected: While specific OEM values for the 09D sensor are not consistently published, typical inductive speed sensors of this type have a resistance in the range of 250-600 Ohms when tested at room temperature. A wide variance is generally acceptable.. Failure: A reading of infinite resistance (open circuit) or zero resistance (short circuit) indicates a failed sensor.

Scan Tool Commands That Help

• VCDS (VAG-COM): Measuring Blocks - Group 001 (Transmission) — This is the primary function to view live data from the transmission sensors. Field 3 typically displays the Output Speed Sensor (G195) reading. This allows a technician to see in real-time if the sensor is sending a signal to the TCM while the vehicle is in motion.
• VCDS (VAG-COM): Clear DTCs — After a repair (like replacing the sensor or fixing wiring), use this function within the transmission control module ( - Auto Trans) to clear the P0720 code. A test drive is then required to see if the fault returns.

Wiring & Ground Locations

• J217 - Transmission Control Module (TCM) — Located under the front passenger seat, beneath the carpet.. This is the module that receives the signal from the G195 sensor. It is notoriously prone to water damage from clogged sunroof drains or AC evaporator drains, which can cause corrosion on the connector pins or internal failure of the module itself, leading to P0720.
• Ground Point 35 — Located under the front passenger's seat, near the TCM.. This is a critical ground connection for components in this area, including potentially the TCM. A corroded or loose ground here can cause a variety of electrical faults, including intermittent or missing sensor signals.
• Main Transmission Connector (T14) — A 14-pin round connector located on the right rear of the transmission housing, often held by a metal C-clip.. This is the main electrical connection point between the internal transmission wiring harness (including the G195 sensor) and the vehicle's main harness going to the TCM. It is highly susceptible to corrosion from road spray and moisture, which can directly cause the P0720 circuit fault.

Real Owner Repair Stories

• OBDII.SHOP Official Blog (Audi Q7 (year not specified)) — Dashboard shift position lights all on, transmission stuck and not shifting properly.
  ❌ Tried (didn't work) Measuring sensor voltage showed the sensors themselves were working.
  ✅ What actually fixed it The fault was traced to the TCM. A specific internal chip on the TCM's circuit board had failed. Replacing this single chip on the board resolved both P0715 and P0720 codes.
• YouTube user 'NO COMMUNICATION TO TCM AUDI Q7' (2014 Audi Q7 3.0T) — No communication with TCM, Check Engine Light on, traction control light on, tire pressure warning on, car would not shift out of Park.
  ❌ Tried (didn't work) Checking fuses, which were all good.
  ✅ What actually fixed it The cause was water ingress in the passenger footwell from a clogged AC drain. This corroded a power wire splice for the TCM located under the carpet. Repairing the corroded splice by soldering the wires restored power to the TCM and fixed all symptoms.
• Ross-Tech Forums user (2011 Audi Q7 3.0 TDI) — Transmission codes, not changing gears.
  ❌ Tried (didn't work) Disassembling and cleaning the multi-function switch, which appeared fine internally.
  ✅ What actually fixed it The 14-pin main transmission connector was found to be badly corroded. The user cut out the factory plug and replaced it with two waterproof Deutsche connectors (a 6-pin and an 8-pin), which resolved the issue.

OEM Part Supersession History

• 09D927321 → 09D927321A, then 09D927321B — Standard part revision and improvement by the manufacturer.
  Heads up: The latest part number, 09D927321B, is the correct service part and is backward compatible with vehicles that used the earlier versions.

Model Year Variations Within This Range

• Approx. 2011-2015: Later models in the first generation could be equipped with an 8-speed ZF transmission (0C8) instead of the 6-speed Aisin (09D). On the 8-speed, the speed sensors are typically integrated into the mechatronics unit or are located differently. While the P0720 code has the same meaning, the physical part location and replacement procedure are entirely different.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Panoramic Sunroof Drain Leaks 🔴 High — Very common across all years. The front drain tubes become clogged with debris, causing water to overflow and leak into the passenger footwell.
• Air Suspension Failures 🔴 High — Common on higher-mileage vehicles (80k+ miles).
• Carbon Buildup on Intake Valves (FSI/TFSI Engines) 🟠 Medium — Becomes a problem typically after 60,000-80,000 miles on direct-injection engines (3.6L FSI, 4.2L FSI, 3.0T TFSI).
• Timing Chain Tensioner Rattle (3.0 TDI) 🔴 High — Often reported on TDI models with over 60,000 miles, especially on cold starts.
• Water Pump Failure (Pre-2015 models) 🟠 Medium — Common failure item, particularly on models with plastic pump housings.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used internal wiring harness or transmission oil pan can be a cost-effective choice if they are in good condition. A used output speed sensor (G195) is a slight gamble but can be viable if from a verified low-mileage donor vehicle.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For wiring harnesses, inspect for any signs of brittleness, cracking insulation, or corrosion on the connector pins.
• For sensors, ensure the connector is not damaged and there is no physical damage to the sensor body.
• Ask for the VIN of the donor car to verify its mileage and check for any reported accidents or flood damage.

OEM-only on this vehicle (don't cheap out):

• Transmission Control Module (TCM) - Due to component protection programming ('immo') that links the module to a specific vehicle, a used TCM cannot be simply swapped in. It would require specialized tools and services to adapt, making a new or professionally refurbished/cloned unit a more reliable choice.

Aftermarket brands forum-validated for this vehicle:

• Bosch (Often the OEM supplier)
• VEMO

Brands owners have reported issues with on this vehicle:

• Unnamed, no-brand sensors from online marketplaces often have high failure rates and may not meet OEM specifications for signal accuracy.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0715 — Input/Turbine Speed Sensor Circuit fault; often appears alongside P0720 when the TCM or internal wiring harness is failing.
• P0721 — Output Speed Sensor Range/Performance; a closely related code often triggered by the same faulty G195 sensor or metallic contamination on the sensor tip.
• P0722 — Output Speed Sensor No Signal; triggered when the TCM receives zero data from the G195 sensor, often due to broken internal wiring or a dead sensor.

Frequently Asked Questions