Value of CEL
01-05-2004, 08:52 PM
#1
Race Car
Thread Starter
Value of CEL
One of my customers R/Rd a '90 964 engine to do a re-seal for oil leaks.
After having re-installed the engine and driving it, the CEL remained
"on". My customer indicated that the engine ran smoothly and had
good power. It didn't appear that there was a problem.
I brought my Porsche Hammer to his location and discovered the CEL
fault was an O2 sensor. Once reset, the CEL fault re-appeared. Upon
reading the O2 sensor via the DME thru the Hammer, the voltage
measured by the DME was .01 to .02 volts which indicated a shorted
O2 sensor or the coax from the sensor to the DME.
Case in Point:
Without the CEL indication, the shop nor end-customer would probably
never have know of the problem. Additionally, the CAT's life may have
been shorted because of the higher CO & HC levels. Although the DME
would disregard the O2 because of the fault (It knows .01 is not valid
and goes to the neutral value of .50 volts.), this problem could have
been costly in the long run. Needless to say, the 964 would have failed
an emissions test.
Bottomline:
If I had a 964, I'd insert a bulb into the CEL position if it didn't have one!
Have Fun
Loren
'88 3.2
After having re-installed the engine and driving it, the CEL remained
"on". My customer indicated that the engine ran smoothly and had
good power. It didn't appear that there was a problem.
I brought my Porsche Hammer to his location and discovered the CEL
fault was an O2 sensor. Once reset, the CEL fault re-appeared. Upon
reading the O2 sensor via the DME thru the Hammer, the voltage
measured by the DME was .01 to .02 volts which indicated a shorted
O2 sensor or the coax from the sensor to the DME.
Case in Point:
Without the CEL indication, the shop nor end-customer would probably
never have know of the problem. Additionally, the CAT's life may have
been shorted because of the higher CO & HC levels. Although the DME
would disregard the O2 because of the fault (It knows .01 is not valid
and goes to the neutral value of .50 volts.), this problem could have
been costly in the long run. Needless to say, the 964 would have failed
an emissions test.
Bottomline:
If I had a 964, I'd insert a bulb into the CEL position if it didn't have one!
Have Fun
Loren
'88 3.2
01-05-2004, 10:10 PM
#3
Race Car
Thread Starter
The CEL is the check engine light which is located in the instrument cluster
unit (pg 374 of "Porsche 911 Enthusiast's Companion") the top picture. It
is the indicator bulb just below the oil temp needle. Some cars have a plug
in the socket which can be later replaced with a bulb.
The CEL is turned "on" by the DME unit when an engine fault has occurred,
e.g. a bad temperature sensor, O2 sensor, or knock sensor. Pgs 8 & 145
of the above book discusses it.
Good Luck
Loren
'88 3.2
unit (pg 374 of "Porsche 911 Enthusiast's Companion") the top picture. It
is the indicator bulb just below the oil temp needle. Some cars have a plug
in the socket which can be later replaced with a bulb.
The CEL is turned "on" by the DME unit when an engine fault has occurred,
e.g. a bad temperature sensor, O2 sensor, or knock sensor. Pgs 8 & 145
of the above book discusses it.
Good Luck
Loren
'88 3.2
01-05-2004, 10:19 PM
#4
I have a 90 C4 and it has Aplug in the CEL socket. If I put in a bulb will I have diagnostic capabilities ie like the later cars or only fault indication. Thanks, Harpreet
01-05-2004, 10:41 PM
#5
Race Car
Thread Starter
You presently have the diagnostic capabilities within the DME. Porsche/Bosch
designed-in that function when they designed the 964 DME electronics.
This is why the DME utilizies three microprocessors versus just one in the
3.2 DME.
Adding the bulb will allow you to know when a DME fault exists versus
having to have a Porsche tester (Hammer) connected to determine this.
Good Luck
Loren
'88 3.2
designed-in that function when they designed the 964 DME electronics.
This is why the DME utilizies three microprocessors versus just one in the
3.2 DME.
Adding the bulb will allow you to know when a DME fault exists versus
having to have a Porsche tester (Hammer) connected to determine this.
Good Luck
Loren
'88 3.2
01-06-2004, 03:14 AM
#6
Loren:
An area of confusion regarding the CEL system seems to be surfacing here with regards to some other posts I've read on this site lately.
FWIW, I have a write up on my (sorry looking) web site which details using the CEL system to extract what codes it can from the DME. There appear to have been several software releases that I know of with regard to the CEL system as follows:
1. On VERY early 964s, like the 1989 models, I believe the system is completely disfuncional, at least on Euro Spec models, and probably US models as well. There may be a functional "dummy" light on some, I just don't remember.
2. 1990 US models for CA have a completely functional CEL system, but other US models supposedly don't. I believe the latter has a CEL "dummy" light that indicates a fault, but isn't capable of producing any codes. The "smart" CEL system, with "smart" meaning the CEL system can be used to extract some codes, became standard on all US models in 1991.
3. ROW spec models seem to have a very unpredictible array of software versions, some with CEL systems (which may only be missing a bulb) where it works as a dummy light once installed, and others where installing the bulb produces unpredictable results. I've never encountered a non-US car that could get the CEL system to produce anything other than a dummy light (i.e., a fault was detected but the codes can't be extracted using the CEL system).
For 1991 and later US models, the "smart" CEL system seems to work quite well. I wouldn't discourage anyone with their CEL bulb disabled from putting a bulb in and trying it out, but I wouldn't tell them to hold their breath, either....particularly if it's a ROW model.
An area of confusion regarding the CEL system seems to be surfacing here with regards to some other posts I've read on this site lately.
FWIW, I have a write up on my (sorry looking) web site which details using the CEL system to extract what codes it can from the DME. There appear to have been several software releases that I know of with regard to the CEL system as follows:
1. On VERY early 964s, like the 1989 models, I believe the system is completely disfuncional, at least on Euro Spec models, and probably US models as well. There may be a functional "dummy" light on some, I just don't remember.
2. 1990 US models for CA have a completely functional CEL system, but other US models supposedly don't. I believe the latter has a CEL "dummy" light that indicates a fault, but isn't capable of producing any codes. The "smart" CEL system, with "smart" meaning the CEL system can be used to extract some codes, became standard on all US models in 1991.
3. ROW spec models seem to have a very unpredictible array of software versions, some with CEL systems (which may only be missing a bulb) where it works as a dummy light once installed, and others where installing the bulb produces unpredictable results. I've never encountered a non-US car that could get the CEL system to produce anything other than a dummy light (i.e., a fault was detected but the codes can't be extracted using the CEL system).
For 1991 and later US models, the "smart" CEL system seems to work quite well. I wouldn't discourage anyone with their CEL bulb disabled from putting a bulb in and trying it out, but I wouldn't tell them to hold their breath, either....particularly if it's a ROW model.
01-06-2004, 03:33 AM
#7
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Dear Loren,
I have to disagree slightly but not totally with what you say. If you are driving along and the O2 sensor fails and the DME picks it and logs a fault it will switch to limp home mode. The 964 will appear to the driver to lose all power. Something is clearly wrong.
Now comes the hard part. If they choose to ignore the problem, shut the engine off and then restart, the failed O2 sensor will not cause this to happen again. However there are other indications, one of course is that you fail your emissions test. In CA as well as in Switzerland. Petrol consumption increases and often after a good drive you will smell petrol. Performance will seem to improve as well especially with the foot down but not full throttle.
Now having the light coming on would avoid this issue if you have a facility locally with a Bosch hammer. You may not be aware of this but finding a repair facility with a Bosch hammer in many parts of your country and others is not easy.
Also if you have an aftermarket chip installed you may get fault code 1141 which is going to keep the light on all the time. Other engine modifications may also cause the light to appear.
Summary: In principle the idea of sticking the light bulb in is great if, you have a stock chip, stock engine and you have access to a repair facility with a Bosch Hammer or the newer KTS500 system. I am sure for your customers in California that this light bulb would be a good idea as long as they know somebody like yourself is offering the troubleshooting service.
However for the rest who maybe do not have emissions requirements, do not have access to a service like you provide and who use rennlist for their troubleshooting it will cause more problems and will not help. If somebody posts on the list that they have a 1990 C2 and they followed the advice and installed a light bulb into the check engine position, and now the light is on. My advice can only be, go find somebody who has a Bosch Hammer. I am afraid I have a problem with this. Bosch hammer owners of course would disagree.
It is up to each owner to decide if they want to know there is a problem, potential problem or not. Remembering that the majority of 964s were built without this CEL system and also remembering the hall sensor will also turn the light on and this is a somewhat unreliable part of the fault code system. Porsche never wanted to activate this system either. It created huge warranty issues for them. Today of course it would generate income if there were any trained 964 mechanics and Bosch Hammer operators around.
Ciao,
Adrian
964C4
PS: You should also be aware that I have worked with onboard diagnostic systems since they were invented. I have a healthy disrespect for the type of diagnostic system used by Bosch in the 964. More modern systems are far more reliable and honest but in the early days they tried to do too much with too little. Porsche even admit to this. I remember a discussion with Honeywell years ago when they sort of admitted without saying anything that they were a sales gimmick and a licence to print money, for Honeywell repair facilities. Over 50% of returned units which indicated a fault were no fault founds.
I have to disagree slightly but not totally with what you say. If you are driving along and the O2 sensor fails and the DME picks it and logs a fault it will switch to limp home mode. The 964 will appear to the driver to lose all power. Something is clearly wrong.
Now comes the hard part. If they choose to ignore the problem, shut the engine off and then restart, the failed O2 sensor will not cause this to happen again. However there are other indications, one of course is that you fail your emissions test. In CA as well as in Switzerland. Petrol consumption increases and often after a good drive you will smell petrol. Performance will seem to improve as well especially with the foot down but not full throttle.
Now having the light coming on would avoid this issue if you have a facility locally with a Bosch hammer. You may not be aware of this but finding a repair facility with a Bosch hammer in many parts of your country and others is not easy.
Also if you have an aftermarket chip installed you may get fault code 1141 which is going to keep the light on all the time. Other engine modifications may also cause the light to appear.
Summary: In principle the idea of sticking the light bulb in is great if, you have a stock chip, stock engine and you have access to a repair facility with a Bosch Hammer or the newer KTS500 system. I am sure for your customers in California that this light bulb would be a good idea as long as they know somebody like yourself is offering the troubleshooting service.
However for the rest who maybe do not have emissions requirements, do not have access to a service like you provide and who use rennlist for their troubleshooting it will cause more problems and will not help. If somebody posts on the list that they have a 1990 C2 and they followed the advice and installed a light bulb into the check engine position, and now the light is on. My advice can only be, go find somebody who has a Bosch Hammer. I am afraid I have a problem with this. Bosch hammer owners of course would disagree.
It is up to each owner to decide if they want to know there is a problem, potential problem or not. Remembering that the majority of 964s were built without this CEL system and also remembering the hall sensor will also turn the light on and this is a somewhat unreliable part of the fault code system. Porsche never wanted to activate this system either. It created huge warranty issues for them. Today of course it would generate income if there were any trained 964 mechanics and Bosch Hammer operators around.
Ciao,
Adrian
964C4
PS: You should also be aware that I have worked with onboard diagnostic systems since they were invented. I have a healthy disrespect for the type of diagnostic system used by Bosch in the 964. More modern systems are far more reliable and honest but in the early days they tried to do too much with too little. Porsche even admit to this. I remember a discussion with Honeywell years ago when they sort of admitted without saying anything that they were a sales gimmick and a licence to print money, for Honeywell repair facilities. Over 50% of returned units which indicated a fault were no fault founds.
Trending Topics
01-06-2004, 08:17 AM
#8
Race Car
Thread Starter
If you're interested in knowing as much as possible about the running
condition of your 964, install a bulb in the check engine light (CEL) socket.
Good Luck
Loren
'88 3.2
condition of your 964, install a bulb in the check engine light (CEL) socket.
Good Luck
Loren
'88 3.2
01-07-2004, 07:52 PM
#9
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Join Date: Mar 2003
Location: Destin, Nashville, In a 458 Challenge
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I kind of like mine off. That way, I am happy, unless the check engine light will confirm that my chip took .3 seconds off my 0 - 60 times. Then there might be good use for it. Just curious though, if it is so important, why did Porsche not hook it up. I may have missed this somewhere.
01-07-2004, 10:31 PM
#10
Race Car
Thread Starter
Why provide more driver info and dealer headaches when the
state/states don't require it? If you were Porsche, would you
connect, if it's not required? I doubt it.
Have Fun
Loren
'88 3.2
state/states don't require it? If you were Porsche, would you
connect, if it's not required? I doubt it.
Have Fun
Loren
'88 3.2
01-08-2004, 04:24 AM
#12
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Dear Doug,
Californian law forced them to connect it for model year 1991. Because Porsche did not want another Califonia only model they connected it for all USA versions. However they did not connect it for the ROW but used the same wiring loom. At least with the 964 they used the same DME (eventually) and always identical engines. The 993 has a different engine and DME for the USA and the ROW. One step forwards and two steps backwards.
Ciao,
Adrian
964C4
Californian law forced them to connect it for model year 1991. Because Porsche did not want another Califonia only model they connected it for all USA versions. However they did not connect it for the ROW but used the same wiring loom. At least with the 964 they used the same DME (eventually) and always identical engines. The 993 has a different engine and DME for the USA and the ROW. One step forwards and two steps backwards.
Ciao,
Adrian
964C4
01-08-2004, 11:40 AM
#14
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Totally driven by emissions laws. The rest of the stuff that comes up is an added bonus. Suitable software capable of flashing codes was available so they stuck it in. Well Bosch did. No point in trying to isolate certain codes and eliminate others.
Ciao,
Adrian
964C4
Ciao,
Adrian
964C4
01-09-2004, 09:28 AM
#15
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CEL
Well.IMHO i must say I think a functional cel/diagnostic system indicator is a worthwhile thing.Like all systems,it is not perfect,but certainly improving.
If the o2 sensor system (or any other sensor for that matter) has failed for any reason I see no problem in having the owner/driver be informed of a problem as soon as it has been detected.Unlike the climate control system,which often stores many faults that are usually false,the dme system is much less prone to do so.The fact is the dme can alert the driver to many other issues,perhaps more pressing then an o2 sensor failure.I also think that although the car will run reasonably well with an o2 sensor system problem,it is clearly not running as well as it could or should.Fuel consumption will suffer,co levels will spike on accel and potential cylinder wash down could occur due to overrich conditions.This will also lead to increased fuel levels in the oil and none of these are desires circumstances in my shop.I know many clients who spend a lot of time and money to achieve and maintain the peak performance and maximum longevity from their Porsches,this is a simple way to that end for most.
Anyway,I do enjoy the discussion,so there are my two cents.have fun,be well and dive carefully,Jerry
If the o2 sensor system (or any other sensor for that matter) has failed for any reason I see no problem in having the owner/driver be informed of a problem as soon as it has been detected.Unlike the climate control system,which often stores many faults that are usually false,the dme system is much less prone to do so.The fact is the dme can alert the driver to many other issues,perhaps more pressing then an o2 sensor failure.I also think that although the car will run reasonably well with an o2 sensor system problem,it is clearly not running as well as it could or should.Fuel consumption will suffer,co levels will spike on accel and potential cylinder wash down could occur due to overrich conditions.This will also lead to increased fuel levels in the oil and none of these are desires circumstances in my shop.I know many clients who spend a lot of time and money to achieve and maintain the peak performance and maximum longevity from their Porsches,this is a simple way to that end for most.
Anyway,I do enjoy the discussion,so there are my two cents.have fun,be well and dive carefully,Jerry