P01A1

Code

Generic P — Powertrain

Alternative Fuel Tank A Pressure Sensor Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 30 EN: 118 RU: 41

AI status

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Page language: EN

Causes

Open or short in sensor wiring (short to battery voltage)
Faulty Alternative Fuel Tank A pressure sensor (internal failure)
Corroded/damaged connector or poor pin contact
Poor or missing ground or reference voltage to the sensor
Actual overpressure in the alternative fuel tank or fuel/EVAP system
Faulty PCM/ECM or intermittent module input

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
Stored/active P01A1 trouble code and freeze frame data available
Possible drivability issues related to fuel system control (varies by vehicle)
Possible difficulty refueling or fuel system warnings (depending on system)
No crank/starting symptoms are uncommon but possible if fuel control is affected

What to check

Retrieve freeze frame and live data with a scan tool; confirm P01A1 is current or historic
Visually inspect wiring and connector at Alternative Fuel Tank A pressure sensor for damage, corrosion, or contamination
Check battery voltage and vehicle grounds (engine and chassis) before testing sensors
Monitor sensor PID on scan tool while key ON engine OFF to see reported voltage/pressure
Check for other related codes (EVAP, fuel pressure, PCM faults) that may indicate system issues

Signal parameters

Typical sensor output voltage range: ~0.0–5.0 V (manufacturer-specific; many sensors 0.5–4.5 V for valid pressure range)
Expected idle/atmospheric pressure voltage: vehicle-specific (check service data), often mid-range
High‑circuit symptom: sensor voltage reported near battery voltage or max scale (e.g., >4.5 V)
Reference supply (if used): usually +5 V reference from PCM — verify present and stable
Ground: low resistance to chassis/PCM ground expected

Diagnostic algorithm

Confirm the code and note freeze frame data: capture sensor PID value, battery voltage and engine conditions when DTC set.
Perform a visual inspection: follow harness from sensor to ECM. Look for chafing, rodent damage, pin corrosion, water intrusion, or crushed wires.
With key ON (engine OFF) monitor the sensor voltage PID with a scan tool. If it reads high (near battery voltage), suspect short to 12V or failed sensor.
Backprobe the sensor connector: measure signal voltage, reference voltage (should be ~5 V if used) and ground continuity. Compare to expected values.
Check wiring for short to battery: with connector disconnected, measure voltage on the signal wire — there should be no battery voltage present. If battery voltage is present with sensor disconnected, trace and repair wiring.
Check for open/short to ground: use an ohmmeter (with battery disconnected) to check continuity from signal wire to PCM and to ground; repair any unexpected shorts/opens.
If wiring and connector look good, apply a known pressure (or vacuum) to the sensor while observing PID to verify sensor output changes smoothly and proportionally. Replace sensor if it fails to respond correctly.
If sensor bench‑tests good but circuit still shows high, inspect PCM power/ground and related modules; consult vehicle-specific wiring diagrams and perform PCM input tests.
After repairs, clear codes and confirm the code does not return during test drive and under the conditions recorded by freeze frame.

Likely causes

Short to 12V on the sensor signal wire (most common for “circuit high” faults)
Failed pressure sensor that is driving output high
Damaged connector (water ingress/corrosion) causing high reading
Loose/poor sensor ground or broken 5V reference to sensor
Less likely: internal PCM input fault

Fault status

⚠️ Status

Circuit High — Alternative Fuel Tank A Pressure Sensor signal higher than expected (possible short to voltage, sensor failure, or actual overpressure).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 2.5 hours