P20AC — Reductant Metering Unit Temperature Sensor Circuit

powertrain (engine/transmission)

Is it safe to drive?

Short-term driving is OK In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

How to diagnose with an OBD scanner

  1. Read the code and freeze frame Connect an OBD2 scanner, confirm P20AC is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the reductant metering unit temperature sensor circuit for damage, corrosion, chafing or poor contact.
  4. Subsystem check Measure reference voltage, ground and signal continuity at the component connector.
  5. Subsystem check Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
  6. Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P20AC does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P20AC (parts and labor, USD, independent shop rates): Repair wiring or connectors: $80–$250; Replace the faulty sensor or actuator: $150–$500; Control module repair: $300–$1,000. Overall, fixing P20AC usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What is the most common cause of P20AC?

The most common causes are: faulty sensor or actuator of the affected circuit, blown fuse feeding the circuit, poor ground connection.

How do I diagnose P20AC myself?

Start with a scan: confirm P20AC, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the sensor and actuator circuits, and verify the suspect component against live data before buying parts.

What does OBD2 code P20AC mean?

Reductant Metering Unit Temperature Sensor Circuit (P20AC): a powertrain (engine/transmission) fault affecting the sensor and actuator circuits. The car is usually drivable while you plan the repair. Most often caused by faulty sensor or actuator of the affected circuit, blown fuse feeding the circuit, poor ground connection.

How much does it cost to fix P20AC?

Repair wiring or connectors — $80–$250; Replace the faulty sensor or actuator — $150–$500; Control module repair — $300–$1,000. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Will P20AC clear itself?

Sometimes P20AC clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

What does P20AC mean?

P20AC (Reductant Metering Unit Temperature Sensor Circuit) is stored when self-diagnostics detect abnormal readings or behaviour of the sensor and actuator circuits. It belongs to the powertrain (engine/transmission) category.

The module monitors this system continuously while driving. When readings fall outside the expected range for a defined number of drive cycles, it stores P20AC and switches on the warning light. Freeze frame data saved with the code shows the exact conditions — rpm, load, temperature, speed — at the moment the fault was detected, which is the best starting point for diagnosis.

Common symptoms of P20AC

  • increased fuel consumption in some cases
  • possible limp mode depending on the affected component
  • Check Engine Light on
  • the affected system operates intermittently or not at all

What causes P20AC?

  • poor ground connection
  • open or shorted wiring in the circuit
  • faulty sensor or actuator of the affected circuit
  • corroded, loose or damaged connector
  • control module driver fault
  • blown fuse feeding the circuit

How to diagnose P20AC

  1. Connect an OBD2 scanner, confirm P20AC is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Visually inspect the wiring harness and connectors related to the reductant metering unit temperature sensor circuit for damage, corrosion, chafing or poor contact.
  4. Measure reference voltage, ground and signal continuity at the component connector.
  5. Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
  6. Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P20AC does not return.

How to fix P20AC

Start with the cheapest and most common causes before replacing expensive parts:

  • Repair wiring or connectors — $80–$250
  • Replace the faulty sensor or actuator — $150–$500
  • Control module repair — $300–$1,000

How much does it cost to fix P20AC?

Repair cost depends on which component actually failed. Typical scenarios for P20AC (parts and labor, USD, independent shop rates):

  • Repair wiring or connectors: $80–$250
  • Replace the faulty sensor or actuator: $150–$500
  • Control module repair: $300–$1,000

Overall, fixing P20AC usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Can you drive with P20AC?

In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

Related OBD2 codes