P1109

Code

OLDSMOBILE P — Powertrain

Secondary Port Throttle System

Brand: OLDSMOBILE

Type: P — Powertrain

Views: UK: 36 EN: 54 RU: 49

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Page language: EN

Causes

Carbon or debris blocking secondary port or linkage
Sticking or seized secondary throttle valve/plate
Faulty secondary throttle actuator (solenoid/motor/servo)
Damaged wiring, poor connector contacts, or short to power/ground in circuit
Faulty throttle position sensor (TPS) or secondary position sensor
Vacuum line leaks or failed vacuum solenoid (if vacuum-operated)

Symptoms

Check Engine Light (MIL) illuminated
Reduced engine performance or 'limp' mode
Hesitation or poor throttle response when accelerating
Unstable or high idle, stalling at idle
No change in secondary port operation when commanded (scan tool tests)

What to check

Read and record all stored/active freeze-frame data and pending codes with a capable scan tool
Check for related codes (TPS, actuator, MAP/MASS) and note freeze-frame RPM/load/temperature
Visually inspect throttle body and secondary port area for carbon, deposits, or foreign objects
Inspect wiring and connectors for the secondary actuator and position sensor — look for corrosion, loose pins, or damaged insulation
Backprobe and monitor relevant PIDs (TPS, secondary position, requested position, actuator current) while commanding changes with a scan tool
Perform a wiggle test on harness while monitoring PIDs for intermittent faults

Signal parameters

Primary TPS closed-throttle voltage typically ~0.2–1.0 V; wide-open throttle ~4.0–4.8 V (values vary by vehicle)
Secondary throttle/port position PID should follow 'Requested Secondary Position' within about 5–10% or a few degrees
Throttle actuator current/pulse duty: normally low at steady positions; may show brief peaks during movement (expected peak varies by design, verify with manufacturer specs)
MAP or intake vacuum should fall (pressure rises) when throttle opens — confirm expected change with accelerator input
No large voltage drops or intermittent supply voltage (should see stable 12 V supply and good ground at actuator/solenoid)

Diagnostic algorithm

Step 1 — Confirm code and freeze-frame: read P1109 and any related codes; note conditions when code set (engine temp, RPM, load).
Step 2 — Visual and basic electrical checks: inspect throttle body, secondary port and linkage for carbon or obstruction; inspect harness/connectors for damage or corrosion. Repair obvious issues and clear codes to retest.
Step 3 — Scan tool PID verification: monitor TPS, secondary position, requested secondary position, throttle actuator current/command while commanding secondary port open/close using bi-directional controls. Verify the actual follows the request.
Step 4 — Power and ground tests: with key on, engine off, verify supply voltage and ground at the actuator/solenoid connector; check continuity to PCM. Repair wiring faults.
Step 5 — Functional tests: with the engine cold/warm as specified, command the secondary port actuator while observing physical movement. If no movement despite correct commands and voltages, suspect actuator mechanical failure. If actuator moves but position PID shows incorrect correlation, suspect sensor or calibration issue.
Step 6 — Vacuum/solenoid test (if applicable): apply vacuum or energize solenoid and confirm port/valve movement; replace failed vacuum components.
Step 7 — Clean or replace: if port/plate is stuck from carbon, remove and clean throttle body/secondary port assembly and retest. If actuator or sensor fails bench or in-vehicle tests, replace the defective component.
Step 8 — Relearn and verify: after repair, clear codes, perform any required throttle/idle relearn procedure per service manual, then road-test to ensure no return of the code.
Step 9 — If problem persists: check PCM inputs/outputs and consider software updates or PCM replacement only after all other components test good.

Likely causes

Carbon buildup or mechanical sticking of the secondary port/throttle plate
Failed or weak secondary throttle actuator (electrical or vacuum)
Wiring connector corrosion, broken wires, or intermittent connection at actuator/sensor
TPS/position sensor out of range or poor correlation with commanded position

Fault status

⚠️ Status

Secondary port throttle system malfunction detected — the secondary intake/throttle port is not operating as commanded or its control/sensor circuit is out of expected range. Inspection of the throttle body, actuator, sensors and wiring is required.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours

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P1109 — Secondary Port Throttle System