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DTC codes / GM codes / P1488

P1488 · GMAuxiliary 5 Volt Supply Output Too Low

P1488 on a GM vehicle means the engine control module (ECM) has detected that the auxiliary 5-volt reference supply it provides to one or more sensors has dropped below the expected operating range. This auxiliary supply feeds sensors such as the fuel tank pressure sensor, the accelerator pedal position sensor, or the air conditioning refrigerant pressure sensor, and a low voltage on that circuit will make those sensors read incorrectly or drop out entirely.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • The check engine light or service engine soon light is illuminated, often with no other noticeable symptoms.
  • The fuel gauge may read incorrectly or the fuel tank pressure sensor may report implausible values, affecting evaporative emission (EVAP) monitoring.
  • The accelerator pedal may feel unresponsive or the engine may enter reduced power mode if the pedal position sensor shares this supply.
  • Air conditioning performance may degrade if the refrigerant pressure sensor loses its reference voltage.
  • Intermittent stalling or rough running can occur if a sensor on the auxiliary 5-volt bus is critical to fuel or air control.
  • Other modules may log communication or sensor reference codes alongside P1488.

Common causes, most likely first

  1. A short to ground on the auxiliary 5-volt reference wire, often where the harness rubs against a bracket or passes through a tight gap.
  2. A failed sensor internally shorting the 5-volt reference to ground, pulling the entire supply low.
  3. Corroded or loose terminals at a sensor connector or at the ECM connector, adding resistance to the reference circuit.
  4. Water intrusion into a connector or sensor housing causing a partial short on the 5-volt line.
  5. A chafed wire in the engine harness near the intake manifold or valve cover where heat and vibration are common.
  6. A faulty ECM internal 5-volt regulator, which is rare but possible after all external circuits are ruled out.
  7. Aftermarket accessories or alarm wiring tapped into the reference circuit and drawing excessive current.

How to diagnose and fix it

  1. Scan all modules and record every stored code, then check the freeze-frame data for P1488 to see which sensor readings were implausible at the time of failure.
  2. Use a wiring diagram to identify every sensor powered by the auxiliary 5-volt reference and unplug them one at a time to see if the reference voltage returns to normal.
  3. Measure the 5-volt reference at the ECM connector with the key on and all sensors connected, then compare it to the specification for your vehicle.
  4. Inspect the harness for chafing, corrosion, and water intrusion at each sensor connector on the auxiliary 5-volt circuit, repairing any damaged wire or terminal.
  5. Perform a voltage drop test on the reference wire and ground circuit to confirm the ECM is not being fooled by resistance in the harness.
  6. Replace the sensor that pulls the reference low when plugged in, then clear the code and verify the 5-volt supply remains stable through a road test.
  7. If every external circuit tests good and the reference still reads low at the ECM, diagnose the ECM power and ground feeds before condemning the module.

What the 5-Volt Reference Circuit Hides

  • A single shorted sensor on the auxiliary 5-volt bus can drag the reference low for every other sensor on that circuit, so the code may point at the ECM when the real fault is one unplugged connector away.
  • Technicians often replace the sensor named in the freeze-frame data first, but the actual short is frequently in a different sensor or in the harness between them.
  • The auxiliary 5-volt supply is separate from the main 5-volt reference used by the throttle position and manifold absolute pressure sensors, so a P1488 does not automatically mean the main reference is bad.
  • Aftermarket remote starters, alarms, and gauge wiring tapped into the reference circuit are a common cause on older GM trucks and SUVs that have been modified.
  • A low auxiliary 5-volt supply can set companion codes in the body control module or fuel system without ever turning on a second warning light, so a full module scan is essential.

Can I keep driving with P1488?

You can usually drive the vehicle to a shop if it runs normally and only the warning light is on, but avoid heavy acceleration or long trips because a failing sensor on this circuit can cause reduced power mode or stalling without warning. If the engine is running rough, stalling, or the pedal feels unresponsive, stop driving and have it towed.

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.

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