Faulty EGR valve position or pressure sensor pulling the 5 volt reference down internally; Damaged, chafed or shorted wiring on the 5 volt reference circuit to the EGR sensor; Corroded, loose or spread terminals in the EGR sensor or valve connector; Another sensor on the shared 5 volt reference circuit shorted, dragging the supply down; Poor engine control module power or ground connections affecting the reference supply; Fault inside the engine control module's 5 volt regulator.

P1403

Loss Of 5 Volts To EGR Sensor.

Pontiac
Powertrain
Manufacturer code
Medium severity

How this code is built

P: SystemPowertrain
1: Defined byThe manufacturer
4: AreaAuxiliary emission controls
03: FaultThe specific fault in that area

What it means

On a Pontiac, P1403 means the engine control module has detected a loss of the 5 volt reference supply to the EGR sensor. The module expects a steady 5 volts at the sensor, and the fault sets when that voltage is missing or pulled out of range. With the reference lost, the EGR sensor signal cannot be trusted, so the module cannot monitor or control exhaust gas recirculation properly.

Symptoms

Malfunction indicator lamp on
Rough or unstable idle
Hesitation or poor response under light throttle
Pinking or knocking under load
Slightly higher fuel consumption
Failed emissions test

Possible causes

Faulty EGR valve position or pressure sensor pulling the 5 volt reference down internallylikely
Damaged, chafed or shorted wiring on the 5 volt reference circuit to the EGR sensorlikely
Corroded, loose or spread terminals in the EGR sensor or valve connectorlikely
Another sensor on the shared 5 volt reference circuit shorted, dragging the supply downpossible
Poor engine control module power or ground connections affecting the reference supplypossible
Fault inside the engine control module's 5 volt regulatorrare

How to diagnose

Read all stored codes and freeze frame data, and note whether other sensor circuit codes are present that share the 5 volt reference.
Visually inspect the EGR valve, sensor connector and the wiring loom for chafing, heat damage, corrosion or water ingress.
Back-probe the EGR sensor connector with the ignition on and check the reference voltage against the manufacturer's specification for your model and engine.
If the voltage is low, unplug the EGR sensor and recheck. If it recovers, the sensor is the likely fault.
If the voltage is still low, unplug other sensors on the shared reference one at a time to find a short, using the wiring diagram for your model.
Check the reference wire for continuity back to the engine control module and for shorts to ground or to other circuits.
Check the engine control module's power and earth supplies for voltage drop.
Clear the code and road test, rechecking for recurrence and watching the EGR sensor reading on live data.

How to fix

Replace the EGR valve or sensor assembly if it is shorting the reference supply.
Repair or replace damaged wiring on the 5 volt reference circuit.
Clean or repair corroded connector terminals, or replace the connector if the pins are damaged.
Replace any other shorted sensor that is pulling down the shared reference.
Repair poor power or earth connections to the engine control module.
Have the engine control module repaired or replaced only after all wiring and sensors are proven good.

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but book it in soon as poor EGR control can cause rough running, pinking and higher emissions. Avoid heavy loads or long journeys until it is fixed.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.