Hi everyone,

I own a 2019 Mercedes-AMG GLC 63S 4MATIC+ (X253, M177 V8 4.0L biturbo, 510hp), registered in Andorra.

My vehicle has been failing the mandatory technical inspection (ITV) due to a lambda value of approximately 1.08–1.10 measured at idle.
The threshold applied here is the generic European default of 0.97–1.03.

Here is the situation:
- No fault codes (checked with XENTRY at Mercedes dealer)
- No air leaks found (intake, exhaust, turbo hoses all checked)
- No mechanical issues identified
- Injection system cleaned, intake system cleaned
- Engine runs perfectly, no symptoms whatsoever
- Mercedes Andorra spent 6+ weeks on the car and found nothing wrong

My question is: has anyone with a GLC63S, C63S or any M177-powered vehicle ever had their lambda measured during a technical inspection (TÜV, CT, ITV)? What was your lambda value at idle?

I'm trying to determine if 1.08 at idle is within the normal operating range of this engine by design, or if there is a genuine issue that has not been identified yet.

Any experience or data from other M177 owners would be extremely helpful.

Thanks in advance.

 

Ill plug in mine tomorrow morning on a cold start and let you know what my lambda is