The P306D fault code is a specific diagnostic trouble code (DTC) found in Peugeot and Citroën models equipped with DV6 diesel engines (most commonly the 1.6 HDi / e-HDi). The code technically stands for "Information on the current consumed by the injector: Injector 1/4."
In plain English, this means the engine computer (ECU) has detected an electrical anomaly with the Number 1 Cylinder Injector. It is not a sensor failure; it is a failure of the hardware itself or the wiring leading to it.
The module supplies pulsed voltage (typically around 4.5–5V) to each plug. If the channel for cylinder #6 fails internally, the ECU sees a circuit fault.
At first glance, the Peugeot 306 D (specifically the naturally aspirated 1.9-litre diesel, codenamed XUD9) looks like any other 1990s French hatchback. But beneath its slightly droopy plastic bumpers lies one of the most paradoxical engines ever made: a mechanical marvel that is simultaneously immortal and self-destructive.
The Peugeot 306 D (often written P306D) refers to a diesel-powered variant of the Peugeot 306, a compact family car produced by the French manufacturer Peugeot from 1993 to 2002. The 306 range succeeded the popular 305/309 line and competed in the C-segment with rivals such as the Volkswagen Golf, Ford Escort/Focus, and Vauxhall/Opel Astra. The diesel “D” models proved particularly important in Europe, where fuel economy and durability made diesel engines a popular choice for private and fleet buyers alike.
Origins and design
Engine and mechanicals (focus on diesel)
Market role and appeal
Driving experience and long-term ownership
Legacy
Conclusion
In the context of Peugeot vehicles, P306D (often specifically P306D-22) is a diagnostic trouble code (DTC) that signifies a coherence or consistency error between the electronic throttle position and the inlet air pressure. This issue is most commonly reported in modern models like the Peugeot 3008 and 5008. Technical Breakdown
The Engine Control Unit (ECU) constantly compares the angle of the electronic throttle butterfly valve with the readings from the Manifold Absolute Pressure (MAP) sensor. When the air pressure entering the engine does not match what the ECU expects for a given throttle position, it triggers this "coherence" fault. Common Symptoms
Active Cruise Control Fault: Many owners report that this is the first warning to appear on the dashboard.
Engine Management Light (EML): Often follows shortly after the cruise control error. p306d peugeot
Limp Mode: The vehicle may experience a significant loss of power and reduced speed to protect the engine.
Speed Limiter Failure: Like the cruise control, the speed limiter may stop functioning as it relies on accurate throttle data.
City Driving Specifics: Interestingly, some drivers find the fault only occurs at low speeds or idling (around 800 rpm) in heavy traffic, while the car may run perfectly fine for long distances at highway speeds. Potential Causes
Diagnostic discussions on the French Car Forum and JustAnswer UK suggest several likely culprits:
Faulty Electronic Throttle Body: A physical failure or sticking of the butterfly valve, or a malfunctioning internal position sensor.
Inlet Air Pressure (MAP) Sensor: A faulty or contaminated sensor sending incorrect pressure readings to the ECU.
Carbon Canister/Solonoid Issues: In some petrol models, a broken carbon canister can cause pressure inconsistencies that trigger the code.
Wiring/Connectors: Corrosion or damaged wiring leading to the throttle body or MAP sensor. Recommended Steps for Diagnosis
Read Live Data: A technician should use a diagnostic tool to monitor the throttle position percentage and inlet air pressure in real-time to see where the mismatch occurs.
Inspect the Throttle Body: Check for carbon build-up or physical obstructions that might prevent the valve from closing or opening smoothly.
Check for Air Leaks: Ensure there are no vacuum leaks in the intake system that could cause unexpected pressure drops.
Software Update: Occasionally, these "coherence" issues can be resolved with an ECU software update from a Peugeot dealership if the manufacturer has revised the sensor tolerance levels. P306D-22 coherence problem - Page 2 - French Car Forum
The Peugeot fault code (often specifically ) relates to coherence issue
between the electronic throttle housing position and the inlet air pressure The P306D fault code is a specific diagnostic
. Essentially, the car's Engine Control Unit (ECU) detects that the physical position of the throttle valve does not match the air pressure readings it expects. Common Symptoms Engine Management Light (EML):
The orange engine warning light illuminates on the dashboard. Limp Mode:
The vehicle may enter a restricted performance mode to protect the engine, often limiting RPM or disabling the turbocharger. System Failures:
Owners frequently report secondary faults like "Active Cruise Control Fault" or speed limiter failure occurring just before the engine light. Erratic Idle/Stalling:
Issues often manifest at low speeds (e.g., in city traffic) or during idle. Potential Causes Faulty Throttle Body (Air Mixer):
The sensor within the electronic throttle housing may be failing or contaminated. Inlet Air Pressure (MAP) Sensor:
A faulty or dirty Manifold Absolute Pressure (MAP) sensor can provide incorrect data to the ECU. EVAP System Issues:
A broken purge valve or a failing carbon (EVAP) canister can cause air pressure discrepancies, specifically at low speeds or idle. Wiring/Connectors:
Corrosion or damage to the wiring harness and plugs can cause intermittent signal loss. Peugeot 306 Owners Club Recommended Troubleshooting Scan the ECU: OBD2 diagnostic scanner like those used by Meta Mechanics
to confirm if the code is persistent and check for accompanying "ghost" codes. Inspect Sensors:
Check the throttle body and MAP sensor for carbon buildup or electrical damage. Check the EVAP Solenoid:
On models like the 508 or 3008, the solenoid valve (often part number V759557380
) located under the air filter box is a known failure point that triggers this specific code. Clean Connections:
Inspect the pins on the throttle position sensor (TPS) for water ingress or corrosion, which is a common issue in older models like the 306. Peugeot 306 Owners Club Engine and mechanicals (focus on diesel)
For a permanent fix, it is best to visit a qualified specialist who can perform live data logging to see if the throttle position and air pressure are truly out of sync during driving. Meta Mechanics local Peugeot specialist garages in your area to help diagnose this specific fault? P306D-22 coherence problem - French Car Forum
The P306D fault code on Peugeot vehicles (often appearing as P306D-22) typically indicates a coherence or consistency issue between the electronic throttle housing position and the inlet air pressure. This specific error is common in modern Peugeot and DS models, such as the 508, 308, and DS7 Crossback. Common Symptoms
Active Cruise Control Fault: Often the first warning to appear on the dashboard.
Check Engine Light (EML): Typically follows the cruise control error, especially during low-speed "city" driving.
Limp Mode: The vehicle may enter a restricted power state to prevent engine damage.
Speed Limiter Failure: Disabling of driver assistance systems. Potential Causes & Diagnostic Steps
The error signals that the engine computer is seeing a mismatch between how much air it thinks should be entering (based on throttle position) and how much is actually entering (based on pressure sensors).
Purge Valve / EVAP System: Many owners have successfully resolved P306D by replacing the EVAP purge solenoid valve or the EVAP canister. In models like the 2019 508, this valve is often located beneath the air filter box near the rear of the engine.
Electronic Throttle Body: A faulty or contaminated throttle position sensor can cause incorrect readings, particularly at low speeds.
Inlet Air Pressure Sensor: A failing sensor or a leak in the intake tract can cause "incoherence" in the pressure readings.
Wiring/Connectors: Inspect for corrosion or damage at the throttle body and pressure sensor plugs. Troubleshooting Recommendations
Read Diagnostic Trouble Codes (DTCs): Use a tool like Diagbox to confirm the sub-code (e.g., P306D-22) for more specific guidance.
Inspect the Purge Valve: Given community feedback, check the solenoid valve for proper operation, as it is a frequent culprit for air coherence faults.
Clean the Throttle Body: Ensure there is no carbon buildup preventing the throttle plate from moving smoothly. P306D-22 coherence problem - French Car Forum
Difficulty: Moderate to Hard (V6 engines have limited access). Cost: $20–$60 (OEM plug) + labor.