My tire pressure light keeps going on “Correct Tire Pressure”. Both front tires have 32psi and the rears have 38-40psi. Last year we had a tire going down and the light only came on when one of the tires went below 25psi, Now if one of the front has less than 32 we get a yellow message.
Why ? I need to know the criteria that it uses to send an alert ?
We stopped at the dealership a few months back and ask the service tech to check the pressures, he looked under the gas-flap and read the pressures as 32 front and 40 back. So that’s what he put in. Not sure if that is correct, I though the way that I read it, those were max pressures ?
Now as we drive and the seasons are changing, the fronts flunctuate by a few psi as the temps change. If one goes below 32, we get a messag.
Need to know why its sending a message before I try to correct the problem.
Any help is appreciated.
In addition to agreeing with Purebred’s suggestion, I will add a question:
If the OP sure that the low-pressure warning isn’t related to the inflation pressure in the spare tire?
Agree with @Purebred. Never heard of checking under the gas flap (door?). In the US it is on the drivers side door jamb or the glove box cover, or both. Also add that if the sensors are good, the TPMS may need a re-calibration. Also never heard of passenger car tires requiring 40 psi, I know people who run them that high but I would never go more than 3 above the placard.
The maximum pressure should be on the tire itself . Why would you question the service person after he looked at the tire plaque . You don’t say what year this vehicle is , the tire pressure monitors only last 7 to 10 years , sometimes less . If it is the monitors you need a tire shop to put new ones in . Same for calibration ( or being a Mercedes it might be a dealer item ) .
Simple, the warning light thinks your tire pressure is low. The solution is equally simple. If the pressures are not low, the sensors mounted in the tires of your 8 year old car are going bad and need to be replaced.
The tire pressure warning must illuminate if there is a 20% loss in pressure in any of the road tires.
Because your vehicle has a different tire pressure front/rear, the low pressure thresholds are also different. If the tires are rotated, the sensors for the rear (40 psi) are now in the front and 32 psi is insufficient. Any time the wheels are relocated to a different position on the vehicle the system must be initialized to relearn the base pressure setting.
Failing sensors/batteries won’t send a false low pressure reading, you should see a system malfunction message.
There is a link to the instruction above in post # 9. Appears to be in the instrument cluster information display, access the menu with the steering wheel buttons.
Good advice above. A shop w/the Mercedes scan tool might be able to read out what the car’s computer thinks the tire pressures of each tire are. If you have a problematic sensor inside a tire, that would help you identify which tire it is.
Wow that is high pressure for the rear, but only when you have 5 passengers and 200 pounds of luggage in the trunk. If you are running with just yourself or yourself and a passenger and no more than 100 pounds in the trunk, I’d suggest dropping the rear to 33, or a little over. I’d probably run 35 to 36 all around.
