My daughter's '98 E-320 displayed a Check Engine and a Multifunction Indicator light. She took it to Autozone and they said the computer posted a P0150, P0133 and a P0155 code.
She replaced the fuel cap (the dealer charged her $41 for the thing) and the lights went out. The gasket was a bit beat up, so this was clearly the culpret.

Questions: Could the other codes for the O2 sensor and the EGR valve have been old problems that might have been fixed before she bought the car a year ago and never cleared? Or, will the trouble codes automatically erase when some time has passed?

How, exactly, do you erase fault codes. Postings mention removing the fuse for the computer, but it isn't listed as such on the fuse menu. Is disconnecting the battery the only sure way?

Many thanks for your help.

__________________
'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles

None of your listed codes have anything to do with a bad gas cap!

They are all O2 sensor related. Bosch suggests that their sensors are good for 100K miles, after that they can fail at any time.

Can't imagine anyone paying $40 for a gas cap...can't imagine the dealer marking it up 200% either!

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Ah, the innate bastardliness of inanimate objects! (and overcharging dealers = Smythe in San Jose) I noticed that MBZ offers a replacement gasket for the gas cap for a few dollars-even cheaper!

The car has 90K on it, so O2 sensors will be changed. If I purchase the Bosch #15738 Universal sensors, I can save her about $160 vs the cost of exact replacements.

Questions: Would there be any effective difference between the Universal and the exacts?

How are the trouble codes erased from memory?

__________________
'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles

"How, exactly, do you erase fault codes."


The fault codes are erased using the scanner that reads them. This can be done at a shop, at AutoZone (since you mentioned that's who read them for you), or you can purchase your own scanner.

I use the Dyno Scanner connected to my Treo cell phone. I like this option because I can read the data while driving, and it will give you realtime horsepower curves (I know... it more of a toy than anything).