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Emissions control: EGR, DPF, catalytic converter and AdBlueGeneric OBD-II codeUrgency: Garage soon

P20B9 on Peugeot: causes and affected engines

P20B9 means: reductant heater “A”: open control circuit.[1][2][3] Peugeot has 5 documented faults that can trigger it, across 5 engines, including 1.5 BlueHDi, 1.6 HDi, 2.0 BlueHDi and 2.0 HDi. Only a diagnosis can confirm the cause on your car.

Documented faults
5
that can trigger it
Engines
5
used by Peugeot, with at least one of them
Peugeot models
17
with at least one of these faults
Urgency
Garage soon

5 sourcesHow we work

Documented faults in Peugeot engines that can trigger P20B9

Grouped by engine or model, from most to least important. These are faults with AdBlue: not all of them will necessarily set the code, and only a diagnosis confirms the cause on your car.

Common causes of P20B9 on any make

From most to least likely, according to the sources.

  1. 1Heater circuit wiring or connectors damaged, cut, short-circuited or in poor contact.[1][2][4]
  2. 2Faulty reductant heater.[1][2][4]
  3. 3Blown or interrupted fuse in the control circuit.[1]
  4. 4Faulty heater control module, SCR or engine control unit, or a programming error.[1][2]

What to check first

The first diagnostic steps, from the most likely and cheapest to check to the most expensive.

  1. 1Read all the system codes. If there are other SCR or AdBlue codes, resolve them before continuing with P20B9.[2][4]
  2. 2Visually inspect the heater and its wiring: breaks, damage or corrosion, and burnt or loose connectors. Repair anything damaged.[4]
  3. 3Check the fuse, and the power supply and earth of the control circuit.[1]
Full guide to P20B9: symptoms, diagnosis and whether you can drive

Frequently asked questions

Which Peugeot engines have faults that can trigger P20B9?

1.5 BlueHDi (1 fault), 1.6 HDi (1 fault), 2.0 BlueHDi (1 fault), 2.0 HDi (1 fault) and 2.2 MultiJet / BlueHDi (Stellantis) (1 fault). Each fault has its own page with the affected years and versions, the symptoms and the repair cost.

What does code P20B9 mean on a Peugeot?

Reductant heater “A”: open control circuit. The reductant is AdBlue (urea solution) in the SCR system of diesel engines. The tank includes a heating element that prevents the liquid from freezing (RACE). P20B9 is stored when the control unit detects that the control circuit of heater “A” is open: it sees no voltage on it, or the heater does not respond as commanded. It is a generic OBD-II code: it means the same on a Peugeot as on any other make.[1][2][3][4][5]

Can I keep driving with P20B9?

Garage soon. The sources do not agree on the severity. CarParts rates it as severe because it can disable the SCR and damage the catalytic converter, and advises not driving with the code and taking it to a workshop soon. PartsAvatar mentions only the warning light and that the particulate filter cannot regenerate; CarWiki speaks of an exhaust system working less effectively. RACE adds that faults in the SCR system can give warnings on the instrument panel and even prevent a restart. The prudent course is to diagnose it soon.[1][2][4][5]

Sources

Every fact on this page links to its source. If you find an error, let us know.

  1. OBD DTC Fehlercode P20B9 | Reduktionsmittel-Heizungssteuerung A – offener StromkreisCarWiki.de · Technical documentation · consulted 31 October 2026 · in German
  2. P20B9 Code: Reductant Heater "A" Control Circuit / OpenCarParts.com · Technical documentation · published 19 December 2024 · consulted 31 October 2026
  3. p20b9 Generic DTC: Reductant Heater "A" Control Circuit/OpenDTCSearch.com (OBD Solutions) · Technical documentation · consulted 31 October 2026
  4. P20B9 OBD Error Code: Problem & SolutionsPartsAvatar · Technical documentation · published 2 June 2022 · consulted 31 October 2026
  5. Qué es un catalizador SCR: funcionamiento, AdBlue y mantenimientoRACE · Motoring press · consulted 31 October 2026 · in Spanish