• The Forums are now open to new registrations, adverts are also being de-tuned.

Tyre Pressure linked to Engine Management?

HonourDad

New Member
Joined
Oct 18, 2024
Messages
6
Location
Sussex
Car
Mercedes-Benz C-Class C250d AMG Line 2017
Hi All,

I've just received delivery of a used C-Class Cabrio (W205) and it had both the engine management light and a tyre pressure warning (stating that FR and LB were at 250Kpa and FL and RB were at 260Kpa). However, when I inflated the tyres (which seemed like they were being misreported) and reinitialized them, the engine management light went out.

Is that 'normal' or just coincidence?

I'm worried I've somehow masked an engine issue by reinitializing the tyres.
 
Last edited:
I agree with the above. I've had a few puncture/low trye pressure warnings over the years and more recently our son's MB the other day - a tyre pressure warning light does not affect the EML.
 
kPa now? I suppose that's the wonderful thing about standards - there are so many to choose from :-)
 
Hi All,

I've just received delivery of a used C-Class Cabrio (W205) and it had both the engine management light and a tyre pressure warning (stating that FR and LB were at 250Kpa and FL and RB were at 260Kpa). However, when I inflated the tyres (which seemed like they were being misreported) and reinitialized them, the engine management light went out.

Is that 'normal' or just coincidence?

I'm worried I've somehow masked an engine issue by reinitializing the tyres.

Welcome.

Did you buy the car from a dealer or a trader? If so, then, as a precaution, it is important to make them aware of the EML asap (preferably in writing/email), keeping in mind that having this documented may help in the unlikely event that it turns out to be a major issue and the car needs to be rejected as per your statutory rights under the Consumer Act Rights 2015.

EML can sometime come up and then go away, this isn't necessarily an indication of serious fault. However, if the car is a Diesel, then the potential typical issues are related to the emissions control systems (DPF/AdBlue/Sensors etc), and these can be costly to repair. Personally, I would get the car scanned on STAR, for peace of mind. You may even be able to get this done at the seller's expense. It may show as a 'historic/stored' fault code which will provide some indication as to why the EML came up (though, unfortunately, sometimes the EML does not leave a 'stored' code).
 
Depending on the reason for the EML it may reset by cycling the ignition on /off so maybe it reset itself.

Surprised the TPMS showed a warning at 36 psi.

K
 
kPa now? I suppose that's the wonderful thing about standards - there are so many to choose from

KPa is the international standard unit for pressure measurement so it's technically correct - for men in white coats.

The rest of use PSI or if you must metric units, bar. I'm fine with bar because 250 KPa = 2.5 bar so why cause confusion by adopting KPa when it's really the same unit as bar that everyone is familiar with. Shame on Mercedes for being so silly.
 
KPa is the international standard unit for pressure measurement so it's technically correct - for men in white coats.

The rest of use PSI or if you must metric units, bar. I'm fine with bar because 250 KPa = 2.5 bar so why cause confusion by adopting KPa when it's really the same unit as bar that everyone is familiar with. Shame on Mercedes for being so silly.

When I was in southern Italy with my car, I took it to a local tyre fitter and asked him to pump up the tyres to '36'. He refused. After some back and forth it turned out that they were using bar... and strangely never heard of psi.

On a more serious note, I knew a man who lost several fingers when he was a lad, after being sent to pump up the tyres of a light aircraft. He was given the figures in psi and a pump with gauge calibrated in atm..... obviously, the tyre blew up.

Had it been a truck tyre, the consequences may have been fatal. Which is probably why truck garages have 'cages' for inflating tyres. But I digress ...
 
KPa is the international standard unit for pressure measurement so it's technically correct - for men in white coats.

The rest of use PSI or if you must metric units, bar. I'm fine with bar because 250 KPa = 2.5 bar so why cause confusion by adopting KPa when it's really the same unit as bar that everyone is familiar with. Shame on Mercedes for being so silly.
PSI is just about the right sized unit for road car tyre pressures in my opinion, which usually only need 2 sig. figs. So fractions of a PSI aren't usually needed, and usually a 2-digit integer is sufficient. kPa is too small a unit, since you need to carry around that superfluous 3rd sig. fig. (the 'units' digit, which can usually be zero), and Bar is too big, since a lot of the important information is after the decimal point. It's one of those rare occasions where the imperial unit makes sense! (IMHO :-))
 
Welcome.

Did you buy the car from a dealer or a trader? If so, then, as a precaution, it is important to make them aware of the EML asap (preferably in writing/email), keeping in mind that having this documented may help in the unlikely event that it turns out to be a major issue and the car needs to be rejected as per your statutory rights under the Consumer Act Rights 2015.

EML can sometime come up and then go away, this isn't necessarily an indication of serious fault. However, if the car is a Diesel, then the potential typical issues are related to the emissions control systems (DPF/AdBlue/Sensors etc), and these can be costly to repair. Personally, I would get the car scanned on STAR, for peace of mind. You may even be able to get this done at the seller's expense. It may show as a 'historic/stored' fault code which will provide some indication as to why the EML came up (though, unfortunately, sometimes the EML does not leave a 'stored' code).
Thanks all.

This is essentially what happened. The dealer booked me in for a STAR diagnostic at the local, official Merc Dealership and they spotted both NOx sensor were faulty. £222 for the diagnostic itself (which my dealer has already said they'd pay for), and the quote for NOx repair was £1600 incl VAT. The dealer is seeking authorisation to get that paid too and I expect they will because they've been OK so far. Not to mention as a remote purchase I have 14 days to return with no quibbles. But as I say, I expect it'll just get done. Some othet things came up on the report too that I'm going to look into but the Merc service team didnt raise them as red flags or anything.
 
All equally low!
Is it? 250kPa = 36 PSI which is what it says in the inside fuel flap. Should I be adding a few PSI more for winter? Genuine question as they do look a little softer than I feel comfortable with. Also the Merc service center didn't mention them being low after today's diagnostic visit.
 
Is it? 250kPa = 36 PSI which is what it says in the inside fuel flap. Should I be adding a few PSI more for winter? Genuine question as they do look a little softer than I feel comfortable with. Also the Merc service center didn't mention them being low after today's diagnostic visit.
I took that to be a joke about ‘low standards’, rather than a comment on your tyre pressures.
 
Thanks all.

This is essentially what happened. The dealer booked me in for a STAR diagnostic at the local, official Merc Dealership and they spotted both NOx sensor were faulty. £222 for the diagnostic itself (which my dealer has already said they'd pay for), and the quote for NOx repair was £1600 incl VAT. The dealer is seeking authorisation to get that paid too and I expect they will because they've been OK so far. Not to mention as a remote purchase I have 14 days to return with no quibbles. But as I say, I expect it'll just get done. Some othet things came up on the report too that I'm going to look into but the Merc service team didnt raise them as red flags or anything.

Result! By the sound of it, the seller is a decent firm.

That been said, keep in mind that AdBlue and SCR issues can be difficult to diagnose and resolve, and so once you get the car back, keep an eye on the EML and make sure to document and report back to the seller anything that's untoward.
 
Result! By the sound of it, the seller is a decent firm.

That been said, keep in mind that AdBlue and SCR issues can be difficult to diagnose and resolve, and so once you get the car back, keep an eye on the EML and make sure to document and report back to the seller anything that's untoward.
Once the issue is fixed and paid for I'll reveal the dealership so they can bathe in the glory of positive feedback 😁
 
Is it? 250kPa = 36 PSI which is what it says in the inside fuel flap. Should I be adding a few PSI more for winter? Genuine question as they do look a little softer than I feel comfortable with. Also the Merc service center didn't mention them being low after today's diagnostic visit.
Standards not pressure 👍
 
PSI is just about the right sized unit for road car tyre pressures in my opinion, which usually only need 2 sig. figs. So fractions of a PSI aren't usually needed, and usually a 2-digit integer is sufficient. kPa is too small a unit, since you need to carry around that superfluous 3rd sig. fig. (the 'units' digit, which can usually be zero), and Bar is too big, since a lot of the important information is after the decimal point. It's one of those rare occasions where the imperial unit makes sense! (IMHO :-))

100%

I couldn't find any way to get the pressure shown in PSI in the car (2019 C Class W205), but the Mercedes Me app does allow this so I just look on my phone instead :D
 
On a more serious note, I knew a man who lost several fingers when he was a lad, after being sent to pump up the tyres of a light aircraft. He was given the figures in psi and a pump with gauge calibrated in atm..... obviously, the tyre blew up.

Had it been a truck tyre, the consequences may have been fatal. Which is probably why truck garages have 'cages' for inflating tyres. But I digress ...

Fatal accidents with aircraft tyres are definitely a thing - Delta Airlines had one at Atlanta very recently. Three maintenance workers were changing a tyre - two dead, one seriously injured.
 

Users who are viewing this thread

Back
Top Bottom