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DTC codes / GM codes / P1433

P1433 · GMFuel Level Sensor 2 Circuit High Voltage

P1433 on a GM vehicle means the engine control module (ECM) has detected an abnormally high voltage on the signal circuit for fuel level sensor 2, which is the secondary sender used on vehicles with dual fuel tanks or a saddle-style tank. The ECM expects a voltage within a calibrated range as the fuel level changes, and a reading above the upper limit tells the module the circuit is open, shorted to voltage, or the sensor has failed.

SystemPowertrain
Code typeGM specific
SeverityLow
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • The check engine light or service engine soon light is illuminated on the dashboard.
  • The fuel gauge may read full, empty, or fluctuate erratically instead of showing the actual level.
  • A driver information center message such as 'Fuel Level Sensor Circuit' or 'Service Fuel System' may appear.
  • On dual-tank trucks, the gauge may switch incorrectly between tanks or show an implausible level after refueling.
  • Often no symptoms besides the warning light, especially if the primary fuel level sensor still provides a usable signal.
  • Remote start or fuel-based range calculations may be disabled or inaccurate.

Common causes, most likely first

  1. An open or high-resistance connection in the fuel level sensor 2 signal circuit, commonly at the connector above the tank or at the ECM harness.
  2. A failed fuel level sensor 2 sending unit inside the secondary tank or on the secondary side of a saddle tank, often due to worn resistor tracks or a stuck float.
  3. Corrosion or water intrusion in the sensor connector or wiring harness, particularly on trucks that see road salt or off-road use.
  4. A short to voltage on the signal circuit, which can be caused by chafed wiring rubbing against a metal body panel or frame rail.
  5. A poor ground at the sensor or at the ECM, which raises the reference voltage the module sees on the signal circuit.
  6. A faulty ECM driver or internal pull-up resistor, though this is far less common than wiring or sensor faults.
  7. Aftermarket accessories or trailer wiring tapped into the fuel system harness that introduce voltage or resistance into the circuit.

How to diagnose and fix it

  1. Connect a scan tool and read fuel level sensor 2 voltage and the primary sensor voltage side by side to confirm the fault is isolated to the secondary circuit.
  2. Visually inspect the sensor 2 connector, harness routing, and ground points for corrosion, chafing, or loose pins before condemning any part.
  3. Measure resistance across the sensor 2 sending unit through its full sweep and compare to the GM service specification for that tank position.
  4. Back-probe the signal circuit at the ECM and at the sensor to check for an open or a short to voltage with the key on and the sensor disconnected.
  5. Check the sensor ground circuit for excessive voltage drop under load, repairing any corroded or loose ground connection.
  6. Replace the fuel level sensor 2 sending unit or the complete fuel pump module assembly if resistance testing proves the sensor is out of range.
  7. Clear the code and verify the fuel gauge and scan tool data track correctly through a full sweep before returning the vehicle.

Why sensor 2 faults fool good technicians

  • Many P1433 repairs are misdiagnosed as a failed fuel pump because the secondary sensor is built into the same module assembly, but the pump itself is often working perfectly.
  • A saddle-style tank can set P1433 when the transfer pump or jet pump fails, causing the secondary side to run dry and the float to sit at a position that produces an out-of-range signal.
  • The code can be set by a simple loose ground at the frame rail near the tank, so always check grounds before dropping the tank for a sensor replacement.
  • On dual-tank GM trucks, the fuel gauge may still read normally because the ECM blends both sensor signals, so the driver may never notice a level problem.
  • Aftermarket remote start or alarm wiring tapped into the fuel level circuit is a frequent cause of high-voltage codes that appear only after the accessory is installed.

Can I keep driving with P1433?

The vehicle remains safe to drive because P1433 affects only fuel level reporting and does not alter engine fueling or safety systems. Avoid relying on the fuel gauge for range, and refuel before the tank drops below a quarter until the circuit is repaired.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage