P118B on Opel: How to Diagnose & Fix
Particulate Matter (PM) Sensor Temperature Not Plausible
1 Opel model · 1 documented issue · $200-$600 repair
P118B on Opel by model: symptoms, diagnosis and fix
Euro 6 diesel Zafira Tourer C models with SCR/AdBlue (1.6 CDTi B16DTH and 2.0 CDTi B20DTH/D20DTH) commonly suffer NOx sensor failure. The upstream/downstream NOx sensors degrade and report implausible values, setting catalyst-efficiency and NOx-sensor codes (e.g. P20EE, P229F, P118B) and putting the car into reduced power / limp mode with an emissions warning and a restart countdown in some cases. German owners (motor-talk.de) report this as a known fault from around 80,000 km. NOx sensors are relatively expensive genuine parts and often fail again if cheap aftermarket units are used.
Common Symptoms
- Engine warning / emissions light
- Reduced power / limp mode
- Restart-limit or AdBlue countdown warning
- Stored NOx/SCR fault codes
How to Fix
Diagnose with a scan tool to identify which NOx sensor (position 1 upstream or position 2 downstream) and confirm the SCR catalyst is functioning. Replace the failed NOx sensor with an OE-quality part and clear codes. Verify AdBlue/DEF quality and dosing, and rule out a genuinely degraded SCR catalyst before condemning the sensor.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine 55485493 position-1 NOx sensor for Zafira C 1.6 B16DTH
Zafira C 1.6 B16DTH/B16DTJ, position 1, chassis F1000001-F1999999 or F2000001-F2999999, OE 55485493. Supply VIN; not the D16 branch.
- Genuine 55485442 position-2 NOx sensor for Zafira C 1.6 B16DTH
Zafira C 1.6 B16DTH/B16DTJ, position 2, chassis F1000001-F1999999 or F2000001-F2999999, OE 55485442. Supply VIN; not the D16 branch.
- Genuine 55598161 position-1 NOx sensor for Zafira C 2.0 diesel
Supply VIN and confirm engine/position.
- OE 55598169 position-2 NOx sensor for Zafira C 2.0 B20DTH
Confirm VIN, engine and current supersession; do not infer D20 fitment without EPC confirmation.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (2)
P118B code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P118B mean on a Opel?
P118B stands for "Particulate Matter (PM) Sensor Temperature Not Plausible." P118B is a GM manufacturer-specific code (Chevrolet, GMC, Cadillac diesels) indicating the engine control module detected an implausible temperature reading from the exhaust Particulate Matter (PM/soot) sensor located downstream of the diesel particulate filter (DPF). The PM sensor uses an internal heater and temperature element to monitor soot accumulating between its electrodes; when the reported temperature does not match expected exhaust conditions, the ECM cannot trust the sensor's soot measurement and sets this code, often illuminating the check engine light and disabling proper DPF/emissions monitoring. On Opel it is documented across 1 model: Zafira.
What are the most common causes of P118B?
The most common causes of P118B are: Faulty or aged exhaust particulate matter (PM) sensor, Open, shorted, or chafed wiring in the PM sensor harness, Poor electrical connection or corrosion at the PM sensor connector, Exhaust leak near the PM sensor altering measured temperature, Failed PM sensor internal heater or temperature element, ECM/sensor control unit software or calibration fault (less common). The specific cause varies by vehicle.
How much does it cost to fix P118B on a Opel?
Published repair estimates on Opel range from $200 to $600 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P118B on a different make?
View P118B across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.