piaschulz10
Mercedes B Klasse Hybrid Knock Sensor Issue Resolved
Summary of the thread
A 2022 Mercedes B Klasse hybrid exhibited a malfunction indicator, increased fuel consumption, and uneven idling, initially suspected to be due to a defective knock sensor. Despite resistance checks being within specifications, a potential cable or plug connection fault was considered. Further investigation revealed a corroded pin in the ECU connector, which, once cleaned and re-seated, resolved the issue, eliminating the warning light and restoring smooth engine operation.
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4 comment(s)
piaschulz10 (community.author)
Good point regarding signal integrity under load. I haven't scoped it yet. Where is the knock sensor located? I can't seem to find any wiring diagrams.
ralfbaumann11
Knock sensor location varies slightly by engine variant, but it's usually bolted to the engine block, somewhere near the cylinders, for optimal vibration detection. Given the symptoms and your diagnostics, the sensor itself is unlikely to be the issue. I'd recommend taking it to a workshop.
piaschulz10 (community.author)
You were right. I took it to a workshop. They found a corroded pin in the ECU connector, cleaned it, re-seated the connector, and the warning light is gone. The engine runs smoothly now. Total cost 95€. Thanks for the help.
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MERCEDES
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BKLASSE
ralfbaumann11
Have you scoped the knock sensor signal while the engine is running? Resistance being in spec doesn't rule out signal degradation due to a break in the wire. Also, check the ECU connector pins for corrosion because that can cause issues even if the wiring itself is good.