🔧 Code P1128 – Extended Open Loop Problem
📌 Meaning of Code P1128
Code P1128 is triggered when the Powertrain Control Module (PCM) detects that the engine remains in open loop longer than expected after startup.
Normally, the engine quickly switches to closed loop, where the PCM adjusts the air/fuel mixture based on sensor data. This code therefore indicates a delay or failure in this transition, which can affect vehicle performance and emissions.
⚠️ Possible Symptoms
- 🔥 Engine light on (Check Engine / MIL)
- Hard starting or prolonged idling
- Excessive fuel consumption
- Rough cold operation
📍 Possible Causes of Code P1128
- ⛽ Faulty fuel delivery system
- 🧭 Faulty Manifold Absolute Pressure (MAP) sensor or damaged connectors
- 🔌 Damaged oxygen sensor (O2) wiring or connectors
- ⚙️ Engine mechanical fault (air intake, valve, etc.)
- 💻 Faulty PCM (rare but possible)
🧰 How to Fix Code P1128?
- Visually inspect the cables, connectors, and components listed above.
- Look for bent, broken, or corroded pins on the MAP and O2 sensors.
- Check fuel delivery:
- Correct fuel pressure
- Clean and functional injectors
- Test the MAP and O2 sensors using a diagnostic tool or multimeter.
- Check engine operation: no air leaks, correct compression.
- As a last resort, test or reprogram the PCM.
💰 What is the Cost to Diagnose Code P1128?
The average diagnostic cost from a professional ranges from €30 to €90, depending on the garage and the complexity of the issue.
If you have an OBD2 scanner and some basic tools, you can perform much of the diagnosis yourself.