Code
P1407
HUMMER
P — Powertrain
EGR Air Intrusion in Exhaust Supply to EGR Valve
AI status
Completed
Completed
100%
Causes
- Leaking or failed EGR tube, pipe, or flange gasket
- Cracked or corroded EGR supply tubing or welds
- Loose or missing clamps/fasteners on EGR/exhaust connections
- Damaged or missing EGR valve gasket or seal
- Intake or exhaust manifold leak upstream of EGR port
- Blocked or damaged EGR cooler (if equipped) causing improper flow
Symptoms
- Check Engine Light (MIL) illuminated
- Rough idle, hesitation, or stumble
- Reduced engine performance or drivability issues
- Poor fuel economy
- Failed emissions test or increased NOx/HC emissions
- Visible soot or exhaust odor near EGR connections
What to check
- Read PCM freeze frame and pending/confirmed DTCs with a scan tool; note operating conditions
- Visual inspection of EGR valve, supply tubing, gaskets, clamps and EGR cooler for soot, cracks or loose fasteners
- Perform an exhaust smoke test or pressurize exhaust supply upstream of EGR to locate leaks
- Backpressure/exhaust flow check upstream of EGR port if applicable
- Check EGR valve operation: commanded vs actual (apply vacuum or use bidirectional scanner)
- Inspect related sensors (EGR position sensor, MAP, intake vacuum) and wiring/connectors
Signal parameters
- EGR commanded position or duty cycle (percent) — should change when commanded by PCM
- EGR position sensor voltage or counts (typical nominal range 0.5–4.5 V depending on design) — changes with valve movement
- Intake manifold vacuum (inHg) or MAP kPa — compare to expected at idle/load
- Exhaust backpressure upstream of EGR (kPa or psi) — low or fluctuating where steady pressure expected may indicate leak
- Scan tool live data: confirm EGR flow/feedback sensors respond when commanded
Diagnostic algorithm
- Verify DTC and note freeze-frame conditions with a scan tool. Check for multiple EGR-related codes.
- Perform a thorough visual inspection of EGR valve, piping, flanges, gaskets, cooler and mounting hardware. Look for soot, cracks or loose bolts.
- With the engine off and cool, pressurize the exhaust supply upstream of the EGR port or use a smoke machine to find intake/exhaust leaks around EGR supply. Repair any leaks found.
- Command the EGR valve open/closed with a bidirectional scan tool while observing EGR position sensor and intake/exhaust parameters. Confirm valve moves and feedback changes.
- If EGR cooler equipped, inspect for internal damage or bypass; remove and inspect if necessary.
- Check for proper sealing at EGR valve to intake manifold flange; replace gaskets and torque fasteners to spec if leaks present.
- If mechanical repairs do not clear the code, inspect wiring, connectors and test EGR position sensor and related sensors for correct operation; replace only if out of specification.
- After repairs, clear codes and perform a road/drive cycle or readiness test to confirm the fault does not return. Retest smoke/pressure if intermittent symptoms persist.
- Safety note: allow exhaust system and engine components to cool before disassembly; use appropriate personal protective equipment.
Likely causes
- Failed or leaking EGR/exhaust supply gasket or flange (most common)
- Cracked EGR supply tube or loose clamp at flange
- Exhaust manifold leak at or near EGR supply port
- Clogged/damaged EGR cooler or internal passage allowing bypass
- Electrical/position sensor fault causing false intrusion detection (check after mechanical)
Fault status
Status
EGR Air Intrusion in Exhaust Supply to EGR Valve — PCM detects abnormal air/exhaust leak or pressure condition in the EGR supply that prevents expected EGR flow.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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