P20AF — Reductant Metering Unit Temperature Sensor Circuit High

OBD2 code P20AF flags a problem with the sensor and actuator circuits (reductant metering unit temperature sensor circuit high). The car is usually drivable while you plan the repair. Common culprits: corroded, loose or damaged connector, open or shorted wiring in the circuit, faulty sensor or actuator of the affected 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

Read the code and freeze frame Connect an OBD2 scanner, confirm P20AF is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
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.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the reductant metering unit temperature sensor for damage, corrosion, chafing or poor contact.
Subsystem check With the reductant metering unit temperature sensor disconnected, measure signal voltage at the harness connector: a high reading with the component unplugged indicates a short to power in the harness; if it drops to normal, the component itself is faulty.
Subsystem check Measure reference voltage, ground and signal continuity at the component connector.
Subsystem check Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P20AF does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P20AF (parts and labor, USD, independent shop rates): Control module repair: $300–$1,000; Repair wiring or connectors: $80–$250; Replace the faulty sensor or actuator: $150–$500. Overall, fixing P20AF 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

Is it safe to drive with P20AF?

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 do I diagnose P20AF myself?

Start with a scan: confirm P20AF, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the reductant metering unit temperature sensor, and verify the suspect component against live data before buying parts.

What does OBD2 code P20AF mean?

What is the most common cause of P20AF?

The most common causes are: corroded, loose or damaged connector, open or shorted wiring in the circuit, faulty sensor or actuator of the affected circuit.

Will P20AF clear itself?

Sometimes P20AF 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 P20AF mean?

P20AF is logged by the onboard diagnostics when the sensor and actuator circuits does not behave as expected. The official definition is “Reductant Metering Unit Temperature Sensor Circuit High”. This is a powertrain (engine/transmission) category code.

“Circuit high” means the control module sees a voltage on the reductant metering unit temperature sensor circuit that is above the expected range — typically close to battery voltage. Physically this points to a short to a power feed, a broken ground return, or a failed component pulling the signal line high.

The module monitors this system continuously while driving. When readings fall outside the expected range for a defined number of drive cycles, it stores P20AF 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.

What causes P20AF?

signal wire shorted to battery positive
failed reductant metering unit temperature sensor pulling the signal high
open ground return of the reductant metering unit temperature sensor
blown fuse feeding the circuit
poor ground connection
control module driver fault
corroded, loose or damaged connector
open or shorted wiring in the circuit

Common symptoms of P20AF

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

How to diagnose P20AF

Connect an OBD2 scanner, confirm P20AF is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
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.
Visually inspect the wiring harness and connectors related to the reductant metering unit temperature sensor for damage, corrosion, chafing or poor contact.
With the reductant metering unit temperature sensor disconnected, measure signal voltage at the harness connector: a high reading with the component unplugged indicates a short to power in the harness; if it drops to normal, the component itself is faulty.
Measure reference voltage, ground and signal continuity at the component connector.
Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P20AF does not return.

How to fix P20AF

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

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

How much does it cost to fix P20AF?

Repair cost depends on which component actually failed. Typical scenarios for P20AF (parts and labor, USD, independent shop rates):

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

Overall, fixing P20AF 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 P20AF?