P1409

Code

CADILLAC P — Powertrain

EGR Vacuum System Leak

Brand: CADILLAC

Type: P — Powertrain

Views: UK: 42 EN: 117 RU: 54

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Page language: EN

Causes

Cracked, split or disconnected vacuum hose/line to EGR actuator or solenoid
Faulty EGR vacuum solenoid (stuck, leaking or electrically failed)
Leaking intake manifold gasket or vacuum port
Failed or leaking EGR vacuum actuator/diaphragm
Blocked or damaged vacuum check valve
Loose or corroded electrical connector or wiring to EGR vacuum solenoid

Symptoms

Check Engine Light (MIL) illuminated, P1409 stored
Rough idle or intermittent stalling at idle
Hesitation or poor throttle response under load
Reduced fuel economy
Failed emissions test (increased NOx or failed EGR-related monitors)
Possible engine ping/detonation under certain conditions

What to check

Retrieve DTCs and freeze frame data with scan tool; note conditions when code set
Perform a visual inspection of vacuum hoses, fittings and EGR-related connectors for cracks, disconnection or damage
Operate EGR vacuum solenoid with a scan tool or apply battery power (where safe) and listen/observe operation
Use a handheld vacuum pump to apply vacuum to the EGR actuator and verify it holds vacuum
Perform a smoke test on intake and vacuum system to locate external leaks
Check continuity/resistance and supply voltage at EGR solenoid connector

Signal parameters

EGR vacuum supply pressure (inHg or kPa) at rest and during commanded EGR — should meet manufacturer specification and hold without rapid decay
Vacuum at EGR actuator when commanded (should move actuator and hold vacuum)
EGR vacuum solenoid supply voltage and ground presence (typically battery voltage when commanded)
Solenoid coil resistance (Ω) – compare to spec
PCM commanded duty cycle or ON/OFF state for EGR vacuum solenoid during test
Related sensor data: MAP/MAF, engine RPM, engine load and throttle position during EGR requests

Diagnostic algorithm

Connect a scan tool, verify P1409 and related codes. Record freeze frame and live data during code set.
Visually inspect all vacuum hoses, fittings, clips and check valve between intake manifold and EGR components. Replace any damaged hoses.
With ignition ON (engine OFF), check for vacuum at the manifold vacuum source and continuity to the EGR vacuum solenoid. Repair connectors/wiring as needed.
Apply a handheld vacuum pump to the EGR actuator. Confirm actuator moves and holds vacuum. If it does not hold, replace the actuator/diaphragm.
Command the EGR vacuum solenoid with a scan tool (or apply battery power per service manual) and verify the solenoid opens/closes and passes vacuum to the actuator. Replace solenoid if inoperative or leaking.
Perform a smoke test of the intake and vacuum lines to locate small leaks not visible on inspection. Repair leaks found.
Inspect and clean EGR valve and passages if carbon build-up is present and restricting movement or sealing.
After repairs, clear codes and perform a road/drive cycle and re-check for code reappearance and proper readiness of EGR monitor.

Likely causes

Aged or brittle vacuum hose between manifold and EGR solenoid
EGR vacuum solenoid leaking when commanded closed
EGR actuator diaphragm torn or failed to hold vacuum
Vacuum supply check valve failed allowing backflow or loss of vacuum
Connector corrosion or open/short in solenoid control circuit

Fault status

⚠️ Status

Stored when the PCM detects a leak or loss of vacuum in the EGR vacuum control system that prevents proper EGR valve actuation.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours

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