Code
P1403
PONTIAC
P — Powertrain
Loss Of 5 Volts To EGR Sensor
Views:
UK: 26
EN: 47
RU: 38
AI status
Completed
Completed
100%
Causes
- Open or broken 5 V reference wire between PCM and EGR sensor
- Corroded, loose or damaged EGR sensor connector pins
- Short to ground on the 5 V reference circuit
- Faulty EGR position/feedback sensor
- PCM internal fault or damaged 5 V reference output
- Aftermarket device or recent repair damaged harness or pins
Symptoms
- Check Engine/MIL illuminated with P1403 stored
- Possible reduced EGR function — increased NOx emissions or failed emissions test
- Rough idle, hesitation, or decreased drivability under some conditions
- Reduced fuel economy (in some cases)
- Related EGR or emission system fault codes may be present
What to check
- Retrieve freeze-frame and all codes with a scan tool; note any related EGR or PCM codes
- Visually inspect EGR sensor connector and wiring for damage, corrosion, pin push‑outs, or signs of overheating
- With ignition ON (engine OFF) backprobe the EGR sensor 5 V reference pin and measure voltage — expected ~4.8–5.2 V
- Unplug the EGR sensor and re-check the 5 V reference at the connector to see if the reference returns (rules out sensor short)
- Perform continuity check between the sensor 5 V reference pin and the PCM 5 V reference pin; check for short to ground on that circuit
- Wiggle harness and connectors while monitoring reference voltage/scan data to reproduce intermittent faults
Signal parameters
- EGR sensor 5 V reference (key ON, engine OFF): ~4.8–5.2 V expected
- If shorted to ground: ~0 V on reference line
- With known-good sensor connected, reference should remain ~5 V; sensor signal output will vary depending on sensor type
- Continuity: 5 V reference wire should show low resistance to PCM reference terminal (near-zero ohms for short runs)
Diagnostic algorithm
- Connect a scan tool, record P1403 and any other stored or pending codes and freeze-frame data. Clear codes and attempt to re-run to confirm persistence.
- Visually inspect the EGR sensor connector and wiring harness for damage, heat, fluid intrusion or aftermarket repairs. Repair any obvious damage.
- With ignition ON (engine OFF) backprobe the 5 V reference pin at the EGR sensor connector. Verify ~4.8–5.2 V is present. If present, suspect sensor or signal/sensing circuit rather than harness/PCM output.
- With sensor still connected, unplug it and measure the 5 V reference at the harness connector. If voltage returns (or is present only with sensor unplugged), suspect a shorted/failed sensor pulling the reference down — replace the EGR sensor and retest.
- If no 5 V reference is present at the harness connector, perform continuity check between the harness reference pin and the PCM 5 V reference terminal. Repair open or corroded wiring/connector faults.
- Check for short-to-ground on the reference circuit by measuring resistance from the reference wire to chassis ground (with connector unplugged). High resistance indicates open; near-zero indicates short.
- If wiring and sensor are good and 5 V reference is still absent, suspect PCM 5 V reference driver fault. Before replacing PCM, re-check connectors, harness grounds, and any related fused circuits. Confirm PCM fault per manufacturer procedures.
- After any repair or replacement, clear codes and perform a drive cycle or re-test with a scan tool to verify P1403 does not return.
Likely causes
- Wiring harness chafed or pinched near engine or firewall causing open/short
- Connector corrosion or water intrusion at EGR sensor plug
- EGR sensor failed internally and pulling down reference
- Poor PCM connector connection or PCM damage after an electrical event
Fault status
Status
Loss of 5 volt reference detected on EGR sensor circuit — open/short/connector or sensor/PCM issue.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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