P1109

Code

CADILLAC P — Powertrain

Secondary Port Throttle System

Brand: CADILLAC

Type: P — Powertrain

Views: UK: 26 EN: 36 RU: 32

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Page language: EN

Causes

Failed secondary throttle actuator or motor
Sticking or carbon‑bound secondary throttle plate/port
Open/short or poor connection in wiring harness or connector to throttle actuator/sensor
Faulty throttle position sensor (TPS) or sensor circuit
Vacuum leaks or intake leaks affecting secondary port function
Failed throttle body assembly

Symptoms

Malfunction Indicator Lamp (MIL/Check Engine Light) illuminated
Reduced engine power or limp‑in mode
Poor or unstable idle (high, low, or surging)
Delayed or poor throttle response
Stalling at idle or on deceleration
Diagnostic trouble codes related to throttle/pedal sensors or idle control

What to check

Read and record freeze frame data and related DTCs with a scan tool
Check for additional throttle/pedal/idle codes (e.g., P0120–P0130 range, P2111/P2112)
Visual inspection: connectors, wiring harness routing, signs of corrosion or damage
With ignition ON (engine off) command secondary port/actuator via scan tool and observe movement
Listen for actuator operation during key ON/engine cranking
Inspect and clean throttle body and secondary port for carbon buildup or obstruction

Signal parameters

Throttle position sensor (TPS) reference: 5 V supply from PCM
TPS output nominal range: approx. 0.5–4.5 V across closed to wide open (vehicle‑specific values vary)
Actuator supply: battery/ignition 12 V present at actuator power feed when commanded (confirm with backprobe)
Command signal: PCM may use a PWM/duty cycle to control actuator (0–100% duty)
Idle RPM expected (typical): 600–900 rpm when warm (vehicle specific)

Diagnostic algorithm

Retrieve all DTCs and freeze frame data. Note related codes and conditions when code set.
Inspect wiring and connectors at the throttle body/secondary port actuator for corrosion, bent pins, or damage. Repair any issues.
With key ON engine OFF, verify 5 V reference and ground at TPS connector; measure TPS output while slowly moving throttle (or command with scan tool) to confirm smooth voltage change.
Command the secondary port/actuator with a capable scan tool and observe movement. If actuator does not move, check supply and ground at actuator and continuity to PCM.
If mechanical binding suspected, remove throttle body and inspect/clean secondary port and plate. Check for free movement by hand (per service manual).
Perform resistance/continuity checks for actuator motor windings per manufacturer specs. Repair or replace harness or actuator as needed.
After repairs or cleaning, clear codes and perform relearn/throttle adaptation procedure if required by manufacturer.
Road test under the same conditions that caused the code and verify DTC does not return. If intermittent, perform longer drive cycle and monitor live data.
If wiring and actuator check good but fault persists, consider PCM flash/reprogram or replacement only after confirming external items are good.

Likely causes

Corroded/loose connector or broken wire to the secondary throttle actuator
Secondary throttle plate physically stuck from carbon buildup
Faulty actuator motor (does not move or responds intermittently)
Incorrect TPS signal or lost 5V reference
Failed throttle body requiring replacement

Fault status

⚠️ Status

Secondary Port Throttle System fault detected. The engine control module has identified that the secondary throttle port/actuator or its circuit is not responding within expected parameters. May cause reduced performance or unstable idle; safe operation and further diagnosis required.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5-3.0 hours

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P1109 — Secondary Port Throttle System