99 Boxster Check engine light issue ( Not Normal)
 

Hi everyone,

I have a 99 Boxster with 90k miles. The cel has been on for a few months now. When the codes were checked it threw six codes. One for every o2 sensor and also maf sensor. I replaced all of the 02 sensors, which I thought was really odd that they would all go out at once. We erased the codes and they came back within 10 minutes. So I have just been driving and not worrying about it. This morning I was driving it and it started jerking slightly and got bogged down. Had the codes checked and it was the same codes. I replaced the maf sensor and cleared the codes. The car drives very good now and seems to have fixed the issue, however four 02 sensors, maf sensor and nearly $1000 later I still have a check engine light on. My indie told me he thought there might be a short or broken wire somewhere, probably something to do with the DME or a connection. I am stumped and they are booked up for several weeks. Does anyone have any clue where to begin? What am I looking for, and where? Thanks so much for any help. Surely someone has experienced a similar issue. To reiterate the car runs very good now and is averaging around 25 mpg. :confused:

Without knowing the CEL codes, you are guessing what the problem is.....
Post them here and I'm sure someone will be able to help you.

Yep,
You can spend a lot of money and change a lot of parts but not fix the problem on these cars. The money pit can get real deep, real fast.

A careful diagnosis starts with the symptoms, exact error codes, model, year, mileage, and any recent work done. Get your own code reader and pull the codes, write them down and report back here. Then we can walk you through the process. There are a lot of common problems and easy fixes but you will need the codes first.

Thanks for the responses guys. I will get the exact codes tonight. I know it was for the 02 sensors. One code for each sensor. My mechanic replaced all of them and it threw the exact same codes the next time I drove it. I have tomorrow off and would love to get to the bottom of this tonight and tomorrow. I will get a scanner and post the codes asap. Keep in mind that my mechanic is a Porsche repair specialist and has the very expensive computer to hook up. So, I'm sure his codes are correct and will be much more accurate than what I can get.

Just as a reference point, you should get the exact same codes with a $40 code reader that a shop with a $17,000 a year PIWIS gets; only difference is what is done with that information. Diagnostics is more than reading codes, it is interpreting them.

In all the years I’ve been turning wrenches, I have never seen all four O2 sensors on a car crap out at one time; never………..

Yep,
If all four O2 sensors are barking they are just trying to tell me something. All going bad on the same day never happens so... What are they saying?

a lot of times it's something happening upstream of the sensors that is causing the sensor to get bad readings. The fact that it's getting readings and reporting the inconsistency is proof that the o2 is working properly.

I, too, have never seen all of them fail at one time...

I only got one "my bad" of taking car straight to Indy without letting the board take a peek at my codes first.

Any time something "isn't right" with my car now, it's "to the boards!"

Mechanics (and often the chevy/ford guys for some reason) seem to want to throw o2 sensors at every engine problem... i dunno why.. but it's annoying.

Thanks for the replies everyone. I talked with my mechanic today and he said the codes were for the heater circuit for all 02 sensors. I can get exact codes tomorrow, but that should give us something to go on. The first place he said to check would be the heater circuit. What is he referring to? My bet is there is a short somewhere. :confused:

Update on the codes
 

I got an obdII and the two codes it is showing are p1117 and p1121. I know these are the same codes it had before we replaced the o2 sensors.

P1117 Oxygen Sensor Heating 1 After Catalytic Converter - Below Lower Limit
P1121 Oxygen Sensor Heating 2 After Catalytic Converter - Below Lower Limit

I ordered a new o2 heater circuit relay since it was only $10. Any ideas?

Both codes indicate that the current to the heated O2 sensors on both engine banks is not where it should be. These are typically not a sensor or relay issue, are most commonly a wiring issue; namely high resistance or an interruption of either the heater circuit or sensor wiring. Diagnostic tree in the OBD II manual is to test the sensor (always the first step), then start testing the wiring harness heading to the DME

This is why swapping parts did not fix it, there was probably nothing wrong with the original sensors. the final step in the diagnostic tree says it all, "Repair wiring harness."

Thanks JFP. That's what I'm thinking too. I appreciate the advice. Has anyone had a similar problem from their 99 Box?

+1
Sounds like a failed harness or faulty heating circuit on the new O2 sensors... it happens:

P1117 and P1121
1. Remove connector of 02 sensor 1/2 after catalytic converter.
2. Connect ohmmeter on pin side to pins 1 and 2.
Display: 1.8 - 2.5 ohms at 20°C.
3. Connect ohmmeter on pin side to pin 1 and 02 sensor housing.
Display: infinite ohms

I will try that tomorrow topless. I appreciate the advice. Does anyone know how hard the harness is to replace. Or how much one costs?

Replacing the harness is not the way you want to go, besides being ridiculously expensive, it is not necessary to do the repair. If some wiring is damaged, you just replace that section of wire with aftermarket equivalent materials.

I took a look at the dme and all the wiring in the trunk. Everything looks perfect. Hmm, maybe my mechanic can find something I can't. I will be sure to update once I find something.

You need to be testing continuity and resistance on the specific wires used by each of the sensor heaters; looking at the wire bundles will not tell you much of anything……

I don't know that much about testing continuity and definitely don't have the tools to test this. I am taking it to the shop on Wednesday and will let you know what I find out. Thanks again for the suggestions everyone.

Does anyone know where you can buy a bentley service manual other than online?

I got mine from barnes and noble, but amazon has them and I'm sure they're on eBay. I've got a lightly used one I'll sell ya if you want.

I will check there in the morning. If they don't have it, I will take yours. Pm me a price. Thanks