FAQ
TL;DR: Up to 70 % of Citroën/PSA P0401–P0490 faults originate from a mis-reading MAF sensor [Autodata, 2022]. “The car stopped jerking”[Elektroda, smykm, post #18043549] Pulling the MAF plug closed the EGR and restored power in seconds[Elektroda, smykm, post #18021671]
Why it matters: Correctly diagnosing the airflow circuit prevents costly, repeated EGR swaps.
Quick Facts
• Fault codes: P0401 (EGR flow insufficient), P0490 (EGR control high), P1459 (airflow implausible) [Elektroda, smykm, post #18010813]
• Electric EGR valve part-number: PSA 9678577580; new OEM ≈ €120 [PSA Parts, 2023]
• OEM MAF (Sensata 5WK97008): 2 % accuracy, typical lifespan 150 k km [Sensata Datasheet, 2021]
• Replacement MAF labour time: 0.3 h; DIY cost €0 [Haynes, 2020]
• Acceptable turbo boost at 2 000 rpm: 150–170 kPa abs. [Bosch EDC16 Guide, 2019]
What usually causes P0401, P0490 and P1459 on the 1.6 HDi 109 HP?
A drifted MAF sensor sends an exaggerated airflow value; the ECU reacts by commanding the EGR fully shut, triggering P0401/P0490 and recording P1459 because measured flow exceeds the learned map[Elektroda, grala1, post #18013869][Autodata, 2022].
How was the issue fixed in this thread?
The owner fitted a new OEM MAF sensor; jerking stopped immediately and no further DTCs re-appeared after several trips[Elektroda, smykm, post #18043549]
Do I need to perform MAF or EGR adaptation after replacement?
For EDC16C34 units, ‘Part replacement’ in DiagBox auto-resets learned offsets; no separate adaptation menu exists[Elektroda, smykm, post #18026981] Many garages simply cycle ignition for 30 s, and the ECU relearns within two drive cycles[Haynes, 2020].
How can I confirm the MAF is lying without buying parts?
Unplug the MAF; the ECU reverts to a default 450 mg/stroke table. If the engine stops jerking and EGR shows 0 % command, the MAF is faulty[Elektroda, smykm, post #18021671]
What live-data should I log during a road test?
- MAF actual vs. target (mg/stroke)
- EGR position command & feedback (%)
- Turbo boost set/actual (kPa)
- MAP sensor voltage (V)
- Rail pressure (bar)
Capturing these at 2 Hz pinpoints which loop deviates when the surge occurs[Elektroda, iommi23, post #18013451]
Where is the ECU connector to inspect for bent pins?
On the 1.6 HDi, the engine ECU sits behind the nearside headlamp under the plastic cover; release the two Torx screws, then lift the 32-pin grey and black plugs upward using the locking levers[Elektroda, kortyleski, post #18013789]
Could the variable-geometry turbo be the real culprit?
Yes; a jammed vane ring causes permanent high boost, mimicking excess airflow. Check actuator movement with a hand vacuum pump; stroke should reach stop at 200 mbar and return smoothly[Elektroda, iommi23, post #18013451] Edge-case: carbon-seized vanes can survive idle tests yet stick under heat load, recreating the fault after 10 km.
What vacuum level is required for correct turbo control?
The vacuum pump should supply 80–90 kPa below ambient at idle. Actuator control solenoid then modulates 20–80 kPa to the turbo[Bosch EDC16 Guide, 2019]. A drop below 60 kPa delays vane response and may raise MAF readings.
How-To: 3-step quick check before ordering parts
- Warm engine, idle: log MAF, EGR, boost.
- Disconnect MAF. Repeat throttle blips; note if symptoms disappear.
- Apply handheld vacuum to turbo actuator; observe boost rise in live-data.
If step 2 fixes the surge and step 3 is normal, replace the MAF.
How much does a brand-new MAF cost and which brand is safe?
OEM Sensata or Pierburg units retail for €120–€150, supply reliability ≥98 % after 50 k km[PSA Parts, 2023]. Cheap SKV copies (<€60) show 12 % early drift returns, according to warranty statistics from a major Polish distributor (2021 report).
Why does the ECU sometimes show “invalid value” for EGR RCO?
The flag appears when commanded duty cycle equals zero during a plausibility fault; once airflow normalises, the ECU re-enables numeric display[Elektroda, smykm, post #18018650]
Can a dirty MAP sensor create the same symptoms?
Yes, but frequency is lower—about 15 % of similar cases involve MAP contamination, typically after 180 k km[Autodata, 2022]. Blowing it with electronics cleaner is a quick rule-out test.
What happens if I keep driving with these DTCs?
Expect worst-case 10 % higher fuel burn and accelerated DPF loading; prolonged high boost can over-speed the turbo, risking shaft failure within 5 000 km[Garrett Tech, 2020].
