Edward Liu

Hey guys, I bought a 2001 with about 80k miles from a guy last year at a good price, and after awhile the CEL lit up, and I looked into the error code via Durametrics, and saw error codes P0171, P0136, and P0174 with CEL.



I've tried many ways to get them to go away, also adding a O2 sensor bung, but that didn't make a diff. So after that, I thought perhaps it's the MAF issue, so I bought a new Bosch MAF and replaced it, then cleared engine codes.

It's kind of strange, since I read the actual values of the old and presumed faulty MAF and the new MAF, and the values are the same, so I assume the old one might be good too, but somehow the old one throws a CEL really quickly, and almost certainly after driving the car for a bit and then when idling CEL would come up.

Anyhow, after I replaced the old MAF and cleared engine codes, the CEL didn't come on anymore, but what came on was "Warning battery/generator" light. This is very strange, because before when using the old MAF, this didn't come up at all, and this only showed up using the new MAF.




I read read error codes at this point, and didn't see any code related to the battery. What I did read though, is that there is still the P0171 code (though it didn't throw a CEL.



Can anyone please let me know what needs to be done to fix it atm?

rmc1148

I would replace the o2 sensors if there is no record of that being done also have the battery/charging system checked as a bad battery/alternator can toss odd codes.

Edward Liu

@rmc1148

1. you mean the O2 sensors after the cats, replace them both? or...Also, the best place to buy them (other than ebay of course?)

2. How to check the battery/charging system? I read this could be an alternator issue.

Thanks!

Kevin

This looks like a combination of things. How new is your battery? Is it taking a charge? If's older than 3 years, you might replace it.

Typically when I see all of these codes minus the Alternator, I recommend checking for leaks.. If the Wideband O2's have not been replaced (50K miles or 10 years) you should replace them>pre CAT..

Again, as these cars are aging my recommendation is:

Leak test.. 2 large leaks and 2 to 3 small leaks is the norm. Remove your air box and install a test plugs with air hose connection. Pump up with compressed air to 18PSI (regulated) If you can't get to 18PSI, you have leaks.

Plugs changed Bosch FR6LDC gapped to 0.032 to 0.034" (18K to 20K miles)
Replace the coil packs, every two plug change interval.
Wideband Bosch O2's as I mentioned above.
MAF replacement every 3 to 4 years

Carlo_Carrera

You can get your charging system checked for free at any AutoZone store. Be aware your battery has to be fully charged for the testing to be accurate so charge it up full. If the test shows your battery is bad buy a new one right then and there and install it and have the system checked again.

rmc1148

All good advice other then I do not believe coils need changed that often.

Edward Liu

1. I think it is taking a charge yeah, it hasn't run out of battery, and I think it is probably older than 3 years. but I am looking to get a leak test for sure.
2. I haven't checked for leaks, but I can get to 0.8-1.0 bar w/ no problem, or is that irrelevant?
3. I mean the car is old, perhaps i can just replace out all the O2s? (do I need to replace the post cats as well?)

Edward Liu

@Carlo_Carrera

I'd def like to get them checked, however I'm in Taiwan, so no autozone to just get a free check :-/

Kevin

The resting voltage should be over 12.50 volts. If it's lower you will have issues.

Seeing boost does not rule out possible leaks.

Edward Liu

@Kevin

I checked the bat and it's 12.5V, but it sometimes drop to 12.4 for like a sec.

I also used durametrics and saw that the supply voltage is actually 10.74V, and power supply is 11.02V, both at idle.

The battery the car is using is http://www.mbpartscenter.com/oe-merc...enz/0045418601.

So does it look like it's a battery/alternator issue?

So what I'm curious about is, if assuming the old MAF was faulty, why would replacing it w/ a new MAF cause the warning battery light to come up? and if I'm only seeing P0171, does that mean it can still be a leak?

Anothing thing is that when I check Ready Status - O2 Sensors, it says "No", does that mean O2 sensors are broken?

Carlo_Carrera

Sounds like your regulator or alternator has gone bad. Most likely regulator.

Edward Liu

Okay, so if in that case, can I fix it myself? or should just bring it to a shop?

Macster

More than likely the O2 sensor ready status is not ready because the car has not been driven enough and in the right way for the DME to complete is readiness monitor tests of the sensors (and probably other systems/sensors as well).

I would advise you to address what more and more appears to be a voltage supply problem, with the source most likely with the alternator (or voltage regulator), though the battery may need to be replaced too, then see what else needs attention.

At over 80K miles the O2 sensors are suspect. The ones in my 2003 Turbo tripped the CEL at just over 130K miles. If the sensors in your engine need to be replaced my advice is to replace all 4. This is what I did. I figured they had delivered good service for 130K miles and I got my money's worth out of them, but it was time to forego any sentiment and just replace all of them and begin working on the 2nd 130K miles...

rmc1148

There are some good diys for replacing the regulator which is what I would do, I'm terrible with putting up links but someone will hook you up. I would replace battery if three years old and don't forget to use tender when car sits for more then a few days. Would replace all o2 sensors if the car were mine with 80k miles and no record of then being done= not saying they are all bad.

Carlo_Carrera

You could do it yourself. It is not difficult but it is tricky and very tight working spaces. If you are mechically experienced And have a decent set of tools you should have no trouble. Some of vacuum lines and check valves on the intake piping are a very tight fit and they have be removed and replaced in a specific order.

The one tip I can give you, since I just replaced my regulator two days ago, is to use a rubber mallet to tap the alternator back into place once you have replaced the regulator. The mounting is very snug.