Bill Wagner

Adrian:

You've lost me completely.

When you say "OBC" I'm assuming you're talking about the "On Board Computer" that was an option to display things like miles/gal, estimated miles to fill up, etc. etc. I do not have this option on my car(unless there is something wrong with it and I made the assumption my car is a "normal" 964), and I've never seen it on a 964 .

On page 24/28-33 of my manual it states at the bottom of the page "The flashing code is listed in the Diagnosing/Troubleshooting plan on page D 24/28-7". If you turn to page 24/28-7, you will notice a table. The writers were kind enough to not bother labelling some of the columns. In any case, in bold print is a column describing the item under observation. To the right of it is, what I THINK is the code the CHECK ENGINE LIGHT should produce. I base this on the example in the manual for a bad O2 sensor on page 24/28-33. In this example the code for a bad O2 sensor is 24 (1124 to be exact), which matches the table entry on page 24/28-7. This is an assumption on my part, and it may be incorrect, but why would the writers of the manual refer to this table if the information wasn't there? The column in the table that I'm referring to is the only one that makes sense.

There is something of a problem with your assumption about a "car headed for California" statement. My car was assembled in early 1991...the earliest dates I can trace back are in roughly the second week of January 1991. California has the toughest emission requirements in the U.S.. ANY car originally destined for California could easilly be sold in any state in the U.S.. The first owner of my car bought it from a well known local dealer and it has stayed in this area since. HOWEVER, if you recall, 1991 was a recession year and California was being hit particularly hard by it. The Washington D.C. area is somewhat recession-proof because so many people in this area work for the U.S. government. I think it's entirely possible my car MAY have been re-routed from an original recession-ridden California to the D.C. area. This would not be the first time this has happened.

Please provide me with more information (or where to look for it) regarding the O2-only statement regarding the check engine light. This is important to both of us for the following reasons:

1. I don't want to think I can trouble shoot my car using the check engine light if it only produces the O2 sensor warning, when in fact something else may be wrong and I should be troubleshooting it using other tactics.

2. You're in the process of writing a book and it needs to be accurate. You don't live in this country and if you make assumptions based on things like "California cars", you may well end up putting out misinformation...not a good thing.

This is NOT an attack on you, so please don't take it as such. I want to get to the bottom of this.

You know the 964 better than I do. Could you suggest some sensors that would be easy to access (in other words, from the topside of the engine) that I could "induce" a fault into? I would think the air flow sensor or the intake air temp sensor would be good candidates. It would be interesting to see if the faults show up if I disconnect these items.


Hope to hear from you soon,

Bill Wagner

Adrian

Dear Bill,
The discussion is becoming blurred. Let us go back to the start to determine the points of research required.
1/. The "Check Engine Light" was required to be installed on all 964s delivered to California in 1991. This "Check Engine Light" under Californian law was only required to check for emissions systems failures.
2/. This system was wired up on the 1990 versions USA only as well but my research from the vast majority of owners say when they put a bulb in the system did nothing.
Heresay evidence only.
3/. This system was not wired up in the 1989 C4s but people claim to have this system as well. Heresay again.
4/. It is also claimed by some owners that and supported by pages in the Porsche Maintenance Manual that I do not have that the function of this check engine light has been expanded. Not heresay but no explanation of how this works.
5/. The system is USA only regardless and I cannot get a straight answer from anyone in the USA about the subject. Everyone seems to have a different system installed. I would love to get two sheets of paper with the same system installed.
I want to find out why and how because this is not explained in any detail in my manuals.
I introduced the On Board Computer and DME software levels as a possibility of an explanation for this expansion policy. The 1991 wiring diagrams show the OBC system as an option. Not the "Check Engine Light System" and I cannot see any connection of fault codes inputs to this light yet. Certainly nothing mentioned on the wiring diagrams that this is a databus.
Yours is also a late build 1991 model which means you have ALL the improvements which were gradually brought into production starting in May 1990 airbags, DME software change, June 1990 Airconditioning, July 1990 Plastic Intakes, October 1990 DME software change, Nov 1990 DME software change and suspension change.
The list is much longer with minor changes.
Inbetween all of this are retrofits, pre delivery changes in the USA etc etc which leads to mass confusion.
I am also keenly aware what my book has to be. If I did not care I would not be having these discussions to find the truth or as close as I can get when it comes to manufactured products.
What goes into my book will be what I have proven to myself to be the correct or most correct explanation at this time. I will make assumptions I am sure. Have to. I will make one guarantee though. I will not make the kind of assumptions which have been made by other authors of Porsche books. Pity this advice was not given to them.
Now to checking sensors.
Engine Temp (disconnect the connector)
Airflow sensor (disconnect the connector which also disables the air temp sensor.
O2 sensor, disconnect it. Or freeze spray it, when the engine is warm. Messes up the comparisons.
Fianlly because this is getting too long. Do not put too much faith in such systems anyway. I am, let us put it this way, well aware of these systems. The Porsche version is somewhat crude to say the least. Primeval really. Even the most highly sophisticated systems that I use every day are unreliable and are only of use when there is a hard constant failure. They are a good sales gimmick but not something I would ever recommend you use or rely on except just for fun. Now you can take that or leave it because it is your time and money not mine.
Ciao,
Adrian
911C4

PS: Bill I am missing the entire OBC section. Would you be so kind as to maybe fax it to me. 41718582797 is my fax number. Any explanation of how this system works would be appreciated.

Bill Wagner

Adrian:

DON'T be offended by this! When looking into this issue I stumbled across the following (U.S.) TSB:

Group X, Number 9202, date June 25, 1992.

A quote from this TSB is as follows:

"As of Model Year 1991, all models are equipped with a "Check Engine" light which lights if a component relevant to exhaust emissions fails."

In the U.S., "relevant to exhaust emissions" usually refers to several sensors that an ECU will use to attempt to achieve an optimal fuel/air ratio, hence lower emissions.

I HATE to say this, but often, particularly on older cars there are two situations one can come across when a "check engine" light doesn't seem to be working. One, the obvious one, is that the bulb has burned out. Another, and certainly more devious one, is for a seller to either deliberately disable (i.e. disconnect) the light, or worse yet, re-wire it so it comes on when one of the other "dummy" lights comes on. Tactics like these are usually done by independent (non-Porsche) dealerships who see a check engine light flashing and either don't know how to fix the problem because they have no expertise doing so, or they do know how to fix the problem but choose to let someone disable or "fake" a check engine light because it's cheaper and quicker than fixing the car.....and they're always in a hurry to sell their cars. By the way, these tactics are not limited to Porsches.

I'm not going to dispute any of your claims. The documentation I've seen is contradictory and incomplete...and I'm only looking at U.S. models (in other words, for those of you with '91s with check engine lights that don't work, it may be one of the conditions I described in the preceding paragraph, but it may also be normal). This is something that needs to be determined.

One thing I WILL give to Japanese cars is that their computer systems and monitoring equipment are excellent. When tuning my old '85 MR2 it could detect even the slightest misadjustments by check engine light alone.

Adrian, I will send you a personal e-mail regarding getting the information you need.

Good Luck,

Bill Wagner

Adrian

Dear Bill,
I never said the 1991 models did not have the Check Engine Light hooked up and working. What we do not know is which 1991 models had them fitted as required by California legislation. 1991 versions of the 1990 version or the real 1991 model or both.
What I did say was that the 1989 and 1990 models never had this system installed or activated respectively. What is actually required to make the system work is also unknown at the moment. The 1991 version of the 1990 version has a different DME or may have a different DME to the real 1991 version depending on when it was built. Confused, so am I.
I have already sent you the California Model Only data to you privately,
Ciao,
Adrian
911C4

PS: My book will clearly state that based on the data that I have, there was a 1989, 1990 and 1991 California (and Japan) model only of the 964s. In 1992 this became a Whole USA model.

GeoC2cab

High Guys,
I decided to try again today, so I did and it worked this time, But it didnt only do it once, it did a number of times, 5 then a long flash then 5, another long flash
and some more,,,,as if it was going through a list of read outs,(does the long flash indicate a new read out?). I had absolutly no understanding of which fault was being tested or if the same one was being done over and over. It kept going so i finally shut my key off, I think everything is ok,am I thinking right???????
Thanx for info.......

Bill Wagner

GeoC2Cab:

The code you're receiving means that there are no faults. It's normal. When I want mine to "shut up" I just turn the key to off and then start normally.

Congrats on getting it going.

Bill Wagner

Bill Wagner

Adrian:

The Porsche documentation is clearly contradicting itself. I showed you a Porsche TSB that clearly stated that ALL '91s had the check engine light feature enabled. You've pointed out that there are footnotes in the manuals that imply that this is a California-only requirement. Manuals and I suppose TSBs are not nessecarily perfect. I don't know what's correct. My suspicion is that the statement in the TSB is correct (if it was sold in the US as a '91 model, the check engine light should be fully functional). You NEED to contact either Porsche Cars of North America or Porsche A.G. to get the correct answer. I suspect that if you tell them you're writing a book favorable about one of their cars they will be more than happy to assist you. Who knows....maybe they'll give you a new 996 to play with If by chance they do such a thing (give you a 996) be sure and mention your poor friend, Bill Wagner...he'd like one too!

Best Wishes

Bill Wagner

LarryC

I was going to post a new message, but found this thread so I thought I'd post here.
I have a '91C2 with 92,000 miles. Bought it a year ago, had the 90K service performed at 89,000 miles. Car has been flawless for the past year, including a 950 mile drive from CT to Chicago (I recently relocated here).

About three weeks ago, the car failed the IL emissions test with a high HC reading. I took it straight to my mechanic (a local independent). They checked it out and recommended a new catalytic converter, which they installed. The car still failed the test. While the car was in their possession (about two weeks), the check engine light came on. They further investigated, and found one of the fuel injector connectors was loose/dirty, so they replaced it and checked the others. After some adjustments, the car finally passed the emission test.

I've had the car less than a week, and put maybe 100 miles on it since I picked it up last saturday, and this evening, the check engine light came on solid. This light has never come on since I've owned the car, prior to the new cat.

They told me they checked the O2 sensor and it is OK.

Question- what should I do? I could try to get the readout from the procedure stated in this thread. I am thinking I should bring the car back to the shop, but honestly my confidence in them has waned a bit. The alternative is to take it to a Porsche dealer/shop. Advice please! Thanks.

Bill Wagner

Larry:

By all means, try testing using the check engine light. Since your light came on, we obviously know it's working (the light bulb, that is). The procedure is simple:

1. Get in the car and put the key in but don't turn it yet.
2. Push the accelerator pedal all the way to the floor.
3. Turn the key to the right (like you were getting ready to start the car) but ONLY move it far enough over so that all the dash lights come on (in other words, to the "latch" position just prior to where you would move the key to start the car).
4. The check engine light should flash briefly.
5. Take your foot off the accelerator pedal.
6. Monitor the way the check engine flashes. The code it produces will be four digits, none of them zeros. The only exception to this is if you receive a single flash followed by five rapid flashes, which indicates all is well.
7. The first flash will always be a "1", meaning a single digit.
8. The second flash will most likely also be a "1", but it may be a "2" (two quick flashes).
9. The third and fourth sets of flashes will be the diagnostic code.

Here's an example of what you might see for the code for an intake air temp sensor (code 25):

light on, long pause, light on, long pause, two quick lights on, long pause, five quick lights on. long pause....and this will either repeat or move on to another fault code if you have one.

Each "long pause" is really only 1/2 to 1 seconds and is used to separate the digits. With that in mind when you read the above, you have the code 1125. The second digit can be either a 1 or a 2, with a 1 indicating a constant fault, and a 2 indicating an intermittent fault. I used to think it was always a 1-1 as a separator, but the first digit means it's originatig from a DME monitored sensor, and the second digit means it's a constant fault (code 1) or intermittent (code 2). You may ALSO have more than one fault, in which case you need to count them out until it becomes clear what the pattern is. The check engine light will continue to produce the same patterns until you turn the power completely off. You may want to have a paper and pen handy so you can write the codes down as they show up.

The final two digits of the code always tell which item is bad, and if you have the manuals, they can be found on page 24/28-7 and 24/28-8 of the service manual. A description of how to use the check engine light is shown on page 24/28-33 of the manual. I think once you see it, it will be quite clear, but you do have to sort of "synchronize" yourself with the lights to read them properly.

If you don't have a manual, let me know and I'll post the codes for you.

Good Luck

Bill Wagner

Adrian

Dear Larry,
When a new Kat is installed the C02 adjustment has to be made. This is made inside the throttle body (also called the DME).
Your DME may be picking up a hard fault some of which you can check like the oxygen sensor code 1124. No faults is 1500. However it may be picking up items which are out of adjustment like C02 level is too high.
The adjustments made to make the 964 pass the emssions test may have come back to haunt you.
Another factor is oil. Oil contamination in the throttle body can cause a Mass Airflow Sensor signal output problem whgich may not show up as a direct fault.
The check engine light is on because the DME says something is wrong.
I highly recommend you take it to a facility that knows what it is doing. Get the Hammer installed and have another emissions check carried out. Send invoice to previous facility because I am sure they have done something incorrect here.
The check engine light system is not what I would guarantee. Even if you do recognise a fault I would still have it confirmed by the hammer. Can get expensive otherwise.
From a straight gut feeling I tend to suspect the oxygen sensor. These units have a guaranteed life of around 50K miles and are recommended by Bosch to be replaced every 75K. There are no recommendations by Porsche because they are considered monitored components therefore are "on condition".
Ciao,
Adrian
911C4

PS: There is a huge amount of data regarding these systems installed in other autos on the net. Unfortunately there is almost nothing or less than nothing on the Porsche set up. However the components used are basically identical.
PSS: The Check Engine Light Flashing system actually emmulates the 9268 Flashing Led tester. It turns out that Bosch had been installing this type of function on many other makes long before Porsche introduced it, USA only, 1991 models and up.

LarryC

Bill,
Thanks for your post.. I am at work now but will try the readout proc and post the codes later tonight. I don't have the manuals so your help with interpreting the codes is appreciated.

Adrian: what is "the hammer"?

I also forgot to mention that this car (since I've owned it) has always had the "hard starting when cold" problem described in another post. It cranks fine (has a new starter, and new battery), but does not turn over until at least 2-3 attempts. When I had the 90K service performed (at a highly experience, reputable shop in CT), they checked everything and found nothing wrong.. suggested possible dirty fuel injectors. I have NOT used any additives whatsoever to try to rectify that problem... advice here welcome also.

Thanks!

GeoC2cab

High,
I've been keeping up w/ this thread, and now that i know what im looking at, it seems I do have a fault according to my check engine light, Bill if you could list the codes they would come in handy;even for future use, I've checked with my shop who has the manuals acorrding to my code 1141,
I'm looking at "change computer".Is it nessecary to actually change the brain, i heard these things are expensive,or can the hammer fix it?
A few questions, the light dosent stay on,it goes out as soon as the car starts, it apparently is a constent problem(according to code),,or is it from a earlier date stored in the computer memory,and can it be erased? Would a computer chip have anything to do w/ this? My car has also recently developed the cold start problem, aside from this it runs like a freight train.
My next step is to bring it to a shop with a hammer,but what will they do with the hammer?
thanx in advance Geo.

LarryC

Bill / Adrian:

I've decided to take the car back to the shop tomorrow morning. I too suspect the O2 sensor... I believe the one on my car is the original (car has 92K miles). Can you post the codes for the O2 sensor? I will run the check engine light test tonight... would love to verify that it is the O2 sensor before I have it replaced. Again, the shop tells me they checked it and it is OK. They also told me that they typically do NOT change the CO2 mix when they replace a cat. converter, which conflicts information in a previous post.

Again, this is a very reputable shop in the Chicago area with an almost perfect record in resolving emission-related problems (the state publishes statistics on this here in IL).

Again, I appreciate the help. I've been a Porsche owner since 1998, but am new to Rennlist!

Larry

Adrian

Dear Larry,
O2 flashing code is 1124 for a failure. However if no faults are registered it should flash 1500.
You should be aware that people do play around with the CO2 adjustment especially at emissions check time. Obviously this depends solely on the repair facility used and the 964 owner.
Ciao,
Adrian
911C4

Adrian

Dear Geo,
Fault code 1141 can mean you have an aftermarket chip installed.
Before changing things like the DME you should also carry out a detailed visual inspection of the DME connector (55 pins under the left seat). Corrosion on the pins can cause problems. Also check out relay R41 the DME relay. If power is low to the DME this may also indicate a DME failure.I very much doubt you have a genuine DME failure. They are highly reliable and normally need outside assistance to be damaged. You should also note that any changes to other components can also cause a 1141 fault code. The DME is not that smart. It often cannot tell between an input failure and an output failure. It will tend to fail itself if it does not understand the input signal. What Part Number DME are you using.
Has anyone played around with the DME jumper plugs. Variant and country code. These could also cause the DME to fail itself. These jumper plugs are in the DME wiring loom near the DME under the seat,
Ciao,
Adrian
911C4