P0722
PowertrainOutput Speed Sensor Circuit No Signal
The gearbox output speed sensor has gone completely silent, so the transmission control module has no idea how fast the output shaft is spinning. That sensor is what tells the gearbox when to change up or down and what the car is actually doing on the road. With no signal coming through, the box usually drops into limp mode and refuses to shift properly, and on many cars the speedometer goes dead or starts reading nonsense.
ⓘ Information only. This page provides general educational information about fault code P0722. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0722 mean?
P0722 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Output Speed Sensor Circuit No Signal.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, often alongside a transmission or gearbox fault message on the dash
- • Gearbox stuck in limp mode, typically locked in second or third gear with no upshifts
- • Speedometer reading zero or jumping around erratically even though you're clearly moving
- • Harsh or delayed gear changes, sometimes a thump going into drive
- • Stalling as you come to a stop, because the box can't tell the engine the car has stopped
- • Worse fuel economy from the gearbox holding low gears and high revs
Possible causes
Causes commonly associated with P0722, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Failed output speed sensor, the most common cause. These are exposed to heat and vibration and the internals eventually pack up, giving zero output
- 2. Damaged or corroded wiring and connector at the sensor. The plug sits low on the gearbox and gets road salt, water and oil thrown at it
- 3. Broken signal or earth wire in the harness, often where the loom flexes near the bellhousing
- 4. Lost power supply to the sensor, a blown fuse or a poor earth will leave it dead even if the sensor itself is fine
- 5. Contaminated transmission fluid coating the sensor tip with metallic debris and killing the reading
- 6. Transmission control module fault or software that needs updating, less common but seen on some marques
- 7. Internal valve body or wiring harness failure on gearboxes where the sensor lives inside the casing
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read all stored codes first and note what's keeping it company. P0722 alongside P0720 or P0700 points at the sensor or its circuit, while a pile of solenoid codes shifts the picture toward the valve body
- 2. Get the car up on a ramp and physically inspect the sensor connector and wiring at the gearbox. Unplug it, look for green corrosion, water in the plug, chafed insulation or oil tracking down the wires
- 3. Check the sensor's power supply and earth with a multimeter, you're typically looking for a 5V or 8V feed and a clean earth. No power means a fuse, wiring or relay problem, not the sensor
- 4. Check the transmission fluid level and condition. Burnt smell, dark colour or glittery metal in it tells you the gearbox has internal wear that may be fouling the sensor
- 5. Backprobe the signal wire with an oscilloscope while a helper drives or while the wheels turn on the ramp. A healthy sensor gives a clean repeating pulse that climbs with road speed. A flat line confirms the sensor or its wiring is dead
- 6. Check manufacturer bulletins before condemning anything. Some gearboxes have known harness or valve body faults where swapping the sensor alone won't fix it
Common questions about P0722
What happens if I just carry on driving with it? +
You'll usually be stuck in limp mode, which keeps the car driveable but slow and clattery, holding one gear and revving hard. The bigger worry is the speed signal. On some setups losing the output speed reading can cause an unexpected harsh downshift, and the abruptness of that at speed isn't something you want to be dealing with on a motorway. Short, gentle local trips to get it to a garage are fine. Long fast journeys aren't sensible until it's sorted.
How soon do I need to get this looked at? +
Treat it as a this-week job rather than something you sit on for a month. It won't blow the gearbox up overnight, but driving a transmission that can't read its own output shaft means it's making decisions blind, and the longer it stays in limp mode the more strain you put on the box from the constant high revs and harsh shifts. If the speedo is dead you also can't legally judge your speed, which is its own problem.
Is it the sensor itself or the wiring that's usually to blame? +
More often it's the sensor. They sit in a hot, vibrating spot and the pickup gives up over time, which produces exactly this no-signal code. That said, plenty of P0722s turn out to be a corroded connector or a chafed wire, especially on older cars that have seen a few British winters of salt. Always check the plug and the feed before buying a sensor. The sensor itself is usually low to mid three figures fitted at an independent, wiring repairs often less.
How long does the repair actually take? +
If it's an external sensor and the wiring checks out, a garage can diagnose and swap it inside a couple of hours. A wiring or connector repair is similar once they've traced the fault. Where it gets longer is gearboxes with the sensor mounted internally, which means dropping the pan, draining and refilling the fluid, and possibly disturbing the valve body. That can turn into the best part of a day and a four figure bill on certain European autos.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →