Lambda sensorsGeneric OBD-II codeUrgency: Garage soon
Code P0036: lambda sensor heater control (bank 1 sensor 2)
P0036 means: heated oxygen sensor (lambda sensor) heater control circuit, bank 1, sensor 2.[1][2][3] The engine control unit has detected a fault in the circuit that controls the heater of the rear lambda sensor on bank 1, the one located after the catalytic converter (sensor 2). That heater is a resistor built into the sensor that quickly brings it up to its operating temperature; Wikipedia puts that temperature at about 316 °C, below which the sensor does not measure properly. The control unit drives it with a modulated earth signal, and the code sets when it finds a value in that circuit different from the expected one (open circuit, short circuit or out of range).[1][2][3][4][5][6]
What code P0036 means
The engine control unit has detected a fault in the circuit that controls the heater of the rear lambda sensor on bank 1, the one located after the catalytic converter (sensor 2). That heater is a resistor built into the sensor that quickly brings it up to its operating temperature; Wikipedia puts that temperature at about 316 °C, below which the sensor does not measure properly. The control unit drives it with a modulated earth signal, and the code sets when it finds a value in that circuit different from the expected one (open circuit, short circuit or out of range).[1][2][3][4][5][6]
Because the rear sensor is used mainly to monitor the catalytic converter, the effect is different from that of a front sensor heater. Carista says that what is delayed after a cold start is the monitoring of the catalytic converter and that there are normally no driving symptoms, although the car would not pass an emissions test until the heater check is completed; Autodoc Club, on the other hand, lists higher consumption, worse emissions, rough running and hard cold starts.[1][2][4][7]
Manufacturers divide up the heater monitoring in different ways. In the 2011 Saab 9-5 workshop manual, the P0036, P0037 and P0038 are the control circuit (the circuit voltage deviates from the expected value for 4 s in a row or 50 s cumulatively) and the P0141 is the heater performance (a current of more than 2.5 A or less than 0.25 A). The P0037 and P0038 are the same circuit at low and high level.[3]
It is a generic OBD-II code (it starts with P0), so it means the same on any make; what changes from one car to another is the most likely cause and the way to check it.[8]
Original definition (SAE J2012): HO2S Heater Control Circuit (Bank 1 Sensor 2)[1][2][3]
Codes from the same family
They indicate the same problem in a specific cylinder, bank or sensor. Causes, symptoms and diagnosis are those on this page.
Causes of P0036 and its family
From most to least likely, according to the sources.
- 1Faulty internal heater in the rear sensor: open circuit, internal short circuit or resistance out of specification, or simply an ageing sensor.[1][4][10][12]
- 2Wiring or connectors in poor condition: wires burnt by exhaust heat, broken or short-circuited, and connectors corroded or damaged by road impacts.[1][4][13]
- 3Blown fuse in the heater circuit.[1][4][13]
- 4Heater earth disconnected or in poor condition, or excessive resistance in the earth or control circuit.[12][13][14]
- 5Faulty engine control unit: an unusual cause that is only considered when the sensor, wiring and supply are all fine.[1][15]
Symptoms
- Engine warning light on in the instrument cluster.[1][4][13]Engine warning light: faults that cause it
- Slightly higher consumption and worse emissions values, according to Autodoc Club.[1]Uses more fuel: faults that cause it
- Rough running, loss of power when accelerating and hard cold starts, according to Autodoc Club; Carista, on the other hand, says there are normally no driving symptoms.[1][4]
- The car may fail an emissions test until the heater check is completed.[4]
How to diagnose P0036
In order: from the most likely and cheapest to check to the most expensive.
- 1Read the code with a scan tool, see whether other heater codes are stored (P0141, P0030, P0031, P0032...) and do a road test to see whether it comes back.[2][3]
- 2Check the sensor heater fuse and, if the circuit has one, its relay: it is the quickest and cheapest thing to check. Autodoc Club suggests measuring them with a multimeter with the sensor disconnected.[1][4][9]
- 3Inspect the rear sensor's connector and wiring: corrosion, damaged terminals, wires burnt by heat, chafed or cut. For VAG group cars, Ross-Tech asks for the whole heater circuit to be checked (sensor, wiring, connector and control unit).[1][4][5][9][13]
- 4Disconnect the sensor and use a multimeter to measure the resistance between the terminals of its heater: an infinite reading indicates a burnt-out heater. The correct value depends on the sensor: Carista quotes 8 to 15 Ω cold, HELLA 2 to 14 Ω and the Saab 9-2X manual, less than 30 Ω. Compare it with the figure in your car's workshop manual.[4][7][14]
- 5Check the heater's supply and earth: with the ignition on, battery voltage should reach the supply terminal (the Saab 9-2X manual asks for more than 10 V) and the circuit earth must have continuity (less than 5 Ω in that manual). Some manuals also allow the heater current to be read with the scan tool: more than 0.2 A on the Saab 9-2X.[4][14]
- 6If the control unit's signal to the heater is not what is expected, the Saab 9-2X manual for the P0038 asks for the voltage at its connector and the heater current to be measured, and for the control unit to be replaced if that current exceeds 7 A.[15]
- 7Replace the rear sensor only if the fuse, connector and wiring are fine and the heater resistance is out of specification, and with the part number the manufacturer specifies for your car. Carista and Autodoc Club agree that the sensor is replaced when the heater is open or faulty.[1][4]
Can I keep driving with P0036?
Garage soon
The sources agree that it is not a safety fault, with some nuances. Carista classifies it as low severity and says there are normally no driving symptoms; Autodoc Club says you can drive for a short time but must go to a workshop as soon as possible, and for the P0037 asks for it to be treated with moderate urgency to avoid greater engine damage; for the P0038, Autodoc Club and PartsAvatar warn that leaving it can increase consumption and damage the catalytic converter. Although it is most likely that you will only see the warning light, it should be repaired without leaving it too long.[1][4][9][11][13]
Documented faults related to P0036
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
Engine sensors: the most serious faults by engine and car
- High severityFrequency: Occasional2.0 DTI and 2.2 DTIVP44 injection pump and air mass meter failureGerman Wikipedia documents recurring failures of the Bosch VP44 injection pump and the air mass meter in the early years of this engine. An owner testimony for this engine describes the pump being replaced at 192,500 km, at a cost the owner calls «prohibitive».
- Medium severityFrequency: Common2.0 TDIClogged particulate filter or faulty pressure sensorThe 2.0 TDI's particulate filter clogs if the car mostly makes short journeys, because it never gets to regenerate; sometimes the fault is just the differential pressure sensor. Cleaning it costs around €200 and replacing it, €800 to €3,000.Repair (garage): €800–€3,000
- Medium severityFrequency: Common1.4 and 1.6 8vCrankshaft position sensor failure (TDC sensor)The crankshaft position sensor (capteur PMH, or TDC sensor) appears repeatedly in the reliability sources for the Clio II, the Kangoo I and the Dacia Logan I with this engine, with hard cold starting or stalling as the main symptoms. It is a cheap part, but the failure can leave you stranded.
- Medium severityFrequency: Common1.4 and 1.6 16vCrankshaft position sensor failureThe crankshaft position sensor (capteur PMH) appears repeatedly in the reliability sources for almost every generation with this engine, with hard cold starting, stalling or the car cutting out unexpectedly. It is a cheap part, but the failure can leave you stranded.
Wiring, connectors and short circuits: the most serious faults by engine and car
- Critical severityFrequency: OccasionalBMW N62 / N63Additional turbo coolant pump with a risk of short circuit and fireIn 2011 BMW recalled 5, 6 and 7 Series, X5 and X6 models built between 2007 and 2011 because of the additional turbo coolant pump: moisture, a short circuit and, in extreme cases, a fire. In 2012 there was another campaign for a crack in the pump, with a more robust version.
- Critical severityFrequency: Occasional1.6 GDi híbrido (Kappa)Main relay of the power relay assembly (overheating and fire risk)Yes, on the first units: Hyundai and Kia recalled 2016–2018 Ioniq and Niro hybrids and plug-in hybrids because the main relay that connects the high-voltage battery could come loose, overheat and, in the worst case, cause a fire.
- Critical severityFrequency: Occasional1.6 GDi híbrido (Kappa)Clutch hydraulic actuator (HCA): leak or moisture with risk of short circuit and fireYes, this is the most documented hybrid system fault: the hydraulic actuator that engages the combustion engine with the hybrid assembly has had two recalls (2018 for a leak on the Niro and 2025 for moisture in its electronic board on the Niro, Ceed and XCeed PHEV), with a risk of short circuit and fire.
- High severityFrequency: Occasional1.3 TCeBlown fuel pump fuseOn the Renault Captur II and Clio V with the 1.3 TCe engine, a 20-amp fuse can blow and leave the car without an engine. According to L'argus, in April 2021 this fault still had no factory fix; the official service centre's diagnosis includes checking, and sometimes replacing, the catalytic converter.
- Critical severityFrequency: CommonRover 75Seat SRS connector fault with airbag and seatbelt warning light onAuto Express warns that the Rover 75's seat SRS connector can cause the airbags to fail, and dealers were fixing it with revised connectors. The Dutch APK inspection puts the airbag or seatbelt fault warning among the most frequent defects across almost all series.
- Critical severityFrequency: OccasionalAlfa Romeo GiuliettaShort circuit from badly routed wiring that can prevent gear shifting (KBA campaign, 2010-2015)Yes: according to Germany's KBA, on Alfa Romeo Giulietta cars built between 2010 and 2015 inadequate cable routing could cause a short circuit and, as a result, gear-shift failure.
Frequently asked questions
What is the difference between the P0036, P0037 and P0038?
All three are the same control circuit for the rear bank 1 sensor heater; the P0036 is the general fault and the P0037 and P0038 narrow it down to low and high level. TaT describes the P0037 as a low voltage or a high current in that circuit, normally a short circuit to earth in the wiring or an internally short-circuited heater, and the P0038 as a high voltage, normally an open heater, a disconnected earth or excessive resistance in the circuit. Autodoc Club, on the other hand, attributes the P0038 to excessive current draw or a short circuit in the heater: the sources do not agree on the electrical origin of the high level, and measuring the circuit with a multimeter settles it.[2][9][10][11][12]
What is the difference between the P0036 and the P0141?
Both affect the rear bank 1 sensor heater, but the P0036 points to the control circuit (the circuit voltage deviates from the expected value) and the P0141, to the heater performance. In the 2011 Saab 9-5 workshop manual, the P0141 sets if the heater current is more than 2.5 A or less than 0.25 A.[3]
Can I drive with the P0036 code?
Yes, for a while: Carista classifies it as low severity and says there are normally no driving symptoms, and Autodoc Club says you can drive for a short time but must go to the workshop as soon as possible. While it lasts, the car would not pass an emissions test until the heater check is completed, so it is worth fixing soon.[1][4]
Do I need to replace the rear lambda sensor when I see the P0036?
Not straight away. First the fuse (and relay), connector and wiring are checked, and the heater resistance and the supply and earth of its circuit are measured. The sensor is only replaced if those checks are fine and the heater is out of specification; Autodoc Club suggests replacing it as the first solution, but workshop manuals start with the electrical tests.[1][3][4][14]
What is the lambda sensor heater for?
The sensor only measures oxygen properly when it is very hot (about 316 °C according to Wikipedia). The heater brings it to that temperature in a short time after starting and allows it to be fitted away from the engine's heat.[6][7]
Will I pass the MOT with code P0036?
If the code has switched on the engine warning light, no: with that light on, the inspection records a serious defect, and on Euro 5 and Euro 6 cars the ITV (Spain's roadworthiness inspection, similar to the MOT) also reads the OBD diagnostic system. Repair the fault before you go; clearing the code just before the inspection does not help either, because it counts as a serious defect.[16]
Not sure what is wrong with your car? Describe what you notice in the symptom diagnosis or see all fault codes.
Sources
Every fact on this page links to its source. If you find an error, let us know.
- Código OBD2 P0036: causas, síntomas y cómo corregirloAutodoc Club · Technical documentation · consulted 4 October 2026 · in Spanish
- P0036 — HO2S Heater Control Circuit (Bank 1 Sensor 2)The Automotive Technician (TaT) · Technical documentation · consulted 4 October 2026
- DTC P0036, P0037, P0038, or P0141 (LDK with Turbocharger) (9-5 9650, 2011, 2.0 l petrol) (copia del manual de taller de Saab)Saab WIS Online (Saab Workshop Information System) · Technical documentation · consulted 4 October 2026
- P0036: OBD-II code P0036 flags a fault in the downstream O2 sensor heater circuit on bank 1Carista · Technical documentation · consulted 4 October 2026
- 16420/P0036/000054 - Oxygen (Lambda) Sensor B1 S2: Heating Circuit: Malfunction / OpenRoss-Tech Wiki · Technical documentation · consulted 4 October 2026
- Oxygen sensorWikipedia · Other source · consulted 4 October 2026
- Lambda sensor - cause of failure, testing and troubleshootingHELLA (HELLA Tech World) · Manufacturer · consulted 4 October 2026
- On-board diagnosticsWikipedia · Other source · consulted 4 October 2026
- Código OBD2 P0037: causas, síntomas y cómo corregirloAutodoc Club · Technical documentation · consulted 4 October 2026 · in Spanish
- P0037 — HO2S Heater Control Circuit Low (Bank 1 Sensor 2)The Automotive Technician (TaT) · Technical documentation · consulted 4 October 2026
- Código OBD2 P0038: causas, síntomas y cómo corregirloAutodoc Club · Technical documentation · consulted 4 October 2026 · in Spanish
- P0038 — HO2S Heater Control Circuit High (Bank 1 Sensor 2)The Automotive Technician (TaT) · Technical documentation · consulted 4 October 2026
- Guide To P0038 OBD Error Code SolutionsPartsAvatar · Technical documentation · consulted 4 October 2026
- DTC P0037 HO2S HEATER CONTROL CIRCUIT LOW (BANK 1 SENSOR 2) (9-2X 9346, 2005, 2.0T) (copia del manual de taller de Saab)Saab WIS Online (Saab Workshop Information System) · Technical documentation · consulted 4 October 2026
- DTC P0038 HO2S HEATER CONTROL CIRCUIT HIGH (BANK 1 SENSOR 2) (9-2X 9346, 2005, 2.0T) (copia del manual de taller de Saab)Saab WIS Online (Saab Workshop Information System) · Technical documentation · consulted 4 October 2026
- Desmontando mitos: ¿puede pasar mi coche la ITV con el testigo de «avería motor» encendido?Diariomotor · Motoring press · published 8 March 2021 · consulted 2 October 2026 · in Spanish