P01AA

Code

Generic P — Powertrain

Alternative Fuel Tank Temperature Sensor Circuit

Brand: Generic

Type: P — Powertrain

Views: UK: 21 EN: 31 RU: 23

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Page language: EN

Causes

Open or short in the tank temperature sensor wiring (broken wire, chafed harness)
Corroded, dirty, loose or damaged sensor connector or pins
Failed/contaminated tank temperature sensor (thermistor or sender)
Poor ground or missing reference/pull‑up voltage at the ECM connector
Water intrusion or fuel contamination affecting the sensor
ECM input circuit fault (rare)

Symptoms

Malfunction Indicator Lamp (MIL) illuminated (check engine light)
Stored P01AA and possibly other related codes
Incorrect fuel temperature reading in scan tool/live data (stuck, out of range or fluctuating)
Fuel trim or engine performance faults when the vehicle attempts fuel‑blend compensation
Possible cold/hot start or fuel economy issues when alternative fuel used

What to check

Read and record freeze frame and freeze‑frame conditions; note fuel type and ambient temp
Scan live data for tank temperature sensor value and compare to ambient/engine temps
Inspect wiring and connector at the tank sensor for corrosion, broken wires, pin damage and water intrusion
Check reference voltage and ground at the sensor connector with ignition on
Perform resistance/voltage checks at the sensor and at the ECM connector to isolate wiring faults
Wiggle harness and operate suspension to reproduce intermittent faults

Signal parameters

Typical sensor type: NTC thermistor (resistance changes with temperature) — exact values are manufacturer specific
Expected signal voltage range: ~0.1 to ~4.9 V depending on temperature and ECU pull‑up (value at ~20–25°C often near midscale ≈2–3 V)
Open‑circuit condition: very high resistance (kΩs to MΩs) and signal voltage near pull‑up or diagnostic high value
Short‑to‑ground: near 0 V; short‑to‑battery: near reference/pull‑up voltage (~5 V)
Resistance example (illustrative only): low at high temp, high at low temp — consult service manual for exact ohms vs temperature chart

Diagnostic algorithm

Verify code and record live data: clear codes and re-run to see if P01AA returns. Note fuel type, ambient temperature and operating conditions when fault sets.
Inspect sensor & connector: visually inspect for corrosion, bent pins, water/fuel intrusion, collapsed insulation, and secure mounting. Repair or replace damaged connectors.
Check reference and ground: with key ON (engine OFF), backprobe connector and confirm the ECM reference/pull‑up voltage and ground integrity. Reference usually ~5 V (confirm with service info).
Measure sensor signal: with connector connected, monitor sensor voltage while warming or cooling (room temp, then warm engine or apply heat/cold carefully to sensor). Signal should move smoothly with temperature change.
Resistance check: disconnect sensor and measure resistance vs temperature (compare to spec chart). If out of range or open/short, replace sensor.
Wiring continuity check: if signal/resistance at sensor is correct but ECM sees wrong value, check continuity and resistance between sensor pin and ECM pin. Repair open/short or high resistance in harness.
Wiggle / load test: with backprobes connected, wiggle harness and move vehicle components to try to reproduce intermittent faults; repair chafing/clips as needed.
Check for corrosion/water in tank area: if water or fuel contamination present, drain/flush per manual and replace sensor/connector as required.
Verify ECM input: if wiring and sensor are good and the fault persists, inspect ECM connector for damage and consider ECU bench test or replacement per manufacturer's procedure.
After repairs, clear codes and road test under conditions that previously set the code to confirm repair.