bj

Hi All

I pulled the clock out of the dash and noticed the lights behind the seat belt and airbag were removed. I move 2 unused lights to these positions and they are constantly on. The seat belt light is probably an open circuit to the seat belt clasp sensor but I'm not sure how I'm going to turn off the airbag light other than to remove it as the previous owner did. Anyone know what triggers this warning light. Also on a previous post, I was told where the temperature sensor is in the blower duct but what is the purpose of the resistor which is also mounted in the duct. Any responses to the above questions would be greatly appreciated.

red90C2
Thanx again
bill

Adrian

Dear Bill,
I assume you live in the USA. If you live in Canada you shouldn´t have airbags in a 1990 Canadian only version.
If the USA assumption is correct you have two lights on "Fasten Seat Belt" and "Airbag" because that is the way the US Government required it to be hooked up. If you have an airbag failure the fasten seat belt light is required to tell you to put on your seat belt. Well thatis the theory anyway.
The light bulbs have been removed by the previous owner who is covering up a problem with the 964 Airbag system. Very dirty trick.
Now there is a big rumour going around about a TSB on the clock. I have asked many times about this TSB but I have yet to see a copy. The only reason I have ever found to change the clock is if the warn lights are glowing on but dimly.
What I recommend you do is go to your nearest Porsche dealer, get them to hook up the Bosch hammer and reset the fault in the control unit. If the fault re-occurs then some fault finding is required. The fault can be anything from loss of airbag pressure, bad connector on the airbag (very common) to a failed control unit and very last, very unlikely but not impossibly the clock. Do not forget that your airbags only have a 15 year life maximum.
This system is very hard to troubleshoot yourself. If anyone says to you, according to this change the clock. Ask them to show what this is and please send me a copy. I have the 1994 version of the manuals and there is nothing in there about this clock. Nobody has produced it on this board or elesewhere.
Take care and prove the failed component before buying a new one.
I would advise a system components check to make sure everything is still installed. Airbags, control unit, crash sensors in the trunk (LH and RH)etc. I suspect that the fact that the lights were unfairly removed which is very bad for you the next owner who expects the airbag to work and it won´t (happened to a club collegue of mine) that the problem is expensive.
To your second question. This sensor is actually the Rear Blower Fan Resistor. Think of this as a temperature switch. If the air in the ducting gets too hot, the resistor applies full 12VDC to the blower motor and the blower motor will dump this air overboard. The rear blower fan has two speeds. Low for heating, high for addtional engine cooling. This resistor is very important. Do not disconect it. If you do nothing will work. Does this sensor have the reset switch (CB) installed.
Ciao,
Adrian
911C4

Randall G.

Hello bj,

Well, I suppose I qualify as one of the people spreading the rumor that a faulty clock is a possible cause for the air-bag light staying lit. In the past, I've even referred to there being a TSB, since the dealer wrote in my receipt, "faulty circuit board, clock replaced per tech bulletin." Anyway, my personal experience:

-My air bag light kept coming on. The light was not dim, but full strength. The light was reset twice by my independent mechanic, after checking for fault codes and finding none.

-Each time after being reset, the light came back on ... say, two weeks or a month later.

-Had the car at the dealer, and asked them to look at the air bag light. They simply replaced the clock, referencing a tech bulletin.

-Since the clock was replaced--two years ago--the air bag light has only come on when it is supposed to. That is, after first turning on the ignition.

The "Tech Bulletin" is what Adrian has been unable to locate. I've called the dealer that installed the clock in my car, and they told me there really isn't a TSB on the clock specifically, but rather the replacement is recommended at "the end of the section on troubleshooting the instrument cluster." Unfortunately, Adrian has been unable to find the book/section the dealer told me this information is located in.

A few more things worth mentioning:

-A search of the archives will yield at least two people (maybe more) that had their air-bag light locked-in problem corrected by replacing the clock. One was fairly recent. In this case, the owner was charged the full diagnostic cost, on top of the cost of the clock. Wound up costing him nearly $400. The clock itself is "only" $169.07.

-In my case, I was charged $45 labor plus the cost of the clock. Since we're not talking a lot of money here, I don't believe there's any funny business going on. And, the fact is, my problem is gone. So, my clock was in fact faulty.

-The cost for diagnosing an air bag light seems to vary wildly between dealers. Some people have been charged several hundred dollars, I was only charged $45.

-Some people would rather "roll the dice" and just replace the clock, rather than paying the dealer $200 in diagnostic time, and then possibly be charged for a clock anyway.

-Ideally, if you have a 964 owning friend living nearby, he/she would simply let you swap clocks to see if the light(s) goes away. This approach could be complicated if the errors need to be cleared before the warning light will go out--I don't know the answer to this.

I agree with Adrian--the P.O. removing the bulbs from the clock was a dirty trick. The ways things work in America, I wouldn't be surprised if the P.O. got his *** sued off if a subsequent owner was ever involved in an accident and the air bag didn't deploy.

Of course, by just turning on the ignition, you should quickly realize the air-bag/seatbelt lights are not working or are burned out.

In summary, I would say that I only disagree with Adrian when he writes, with respect to the air-bag light being locked-in, "very unlikely but not impossibly the clock." I think the clock being at fault is not unlikely. This is based on my own experience and what I have read on this board.

bj

Adrian / Randall

I live in Canada. I had the Bosche Hammer put on which alerted me to this problem. I question whether Canadian cars are exempt from having this airbag light, the reason being, since I put a bulb in the socket it has the consistent behavior of illuminating when the key is turned to the 1st position along with all of the other lights, as well it has a slight flicker approximately 10 seconds after the engine starts and an obvious off for 1 second then on constantly from that point on. This consistent behavior leads me to believe that the computer is cycling or polling the sensors and is finding a fault and reporting it by illuminating the airbag light constantly. Where are the sensors in the RHS/LHS and what do they look like?
The blower temperature sensor I was led to believe was the other device in the blower tube above the resistor, the one which releases by a 1/4 turn and has a long snout and 2 wires leading out of it? I put heat to the resistor while I had it out and connected to an ohm meter and there wasn't much deviation between hot and cold.

Thanx for the response, you're a wealth of knowledge...bill

Adrian

Dear BJ,
Do you have airbags installed. Are they Porsche installed or an aftermarket conversion to make this 964 comply with USA laws.
Now you may question whatever you like but the fact is there was a special "no airbag" version of the 964 for Canada only in 1990. It is a pity that you did not provide the whole story in the beginning because your reply has changed everything anyway.
I have all the VINs for these 964s.
Give me the VIN of your 964 and I will tell you if it is among the excempted batch or where it was originally destined for. The other possibility was that this 964 was imported into Canada and the airbags system was disconnected and maybe even partially removed because in 1990 there was no mandatory requirement for airbags.
The sensors are by each strut in the luggage compartment.
The thing about the clock is being lost so I will not explain them anymore. It is not my money.
The sensor you are looking at is the Heating Sensor. This sensor tells the control unit the duct temp of the air it is about to receive. The sole purpose of this sensor is to allow the control unit to adjust the mixing chamber valves to allow the correct amount of outside air to be mixed with heated air to meet the temperature requirements set by the driver. If this sensor does not work the only result is that it takes a little longer to establish the correct internal temperature. This sensor works in conjunction with the other temp sensors in the system.
Ciao,
Adrian
911C4

FlyYellow

I just had the seat belt and air bag warning light come on (both) along with the ! warning light. I too was nervous that the clock was the problem, but took it to my mechanic. he put the bosch hammer on it and it detected a fault on my front passenger sensor. i replaced it and the fault disapeered.

by the way: to replace the air bag sensor was $83 for the part and $25 for the specialized socket.

lear60man

I wish I would have read this list earlier. I had the faces on my gagues changed today and after replacing them, thoes two pesky lights came on. The Spedo shop didn't know why and I left Pi**ed. I went to the dealer and problem gone via the hammer. They explained to me that the clock was part of the airbag system and if you drive it without the clock.....lights come on. FYI

J-McDonald

I had the same experience at Learman -- had my gauges pulled and refinished, only to have the seat belt and air bag lights come (and stay) on. The mechanic said that, in his experience, whenever the gauges come out, it trips the airbag and seatbelt lights (he didn't narrow it to only the clock). I had them hook the hammer up and the problem was fixed immediately.

Adrian

The first action (costs a few bucks) when the airbag and seat belt lights come on, is to get a Bosch Hammer initiated reset. I have helped a few people with this problem recently and not one ended up with a failed clock. 2 bad connectors on the airbag pill, 1 with a bad sensor, one just needed a reset and one with corrosion on the steering column connector which provides the circuit from the control unit to the pill to activate it. Plus the horn whichis the clue here. No horn and airbag/seat belt warn lights, no circuit via these slip rings. You have to remove the steering wheel to get access.
The clock is part of the direct warning system so removing it will disconnect it from the control unit and the control unit will log a fault. A logged fault can normally be only be reset using a Bosch Hammer.
The point to remember is that each fault may well be different as has been detailed inthis thread. The quickest, cheapest and most efficient method of troubleshooting this system is to use the Bosch Hammer.
Ciao,
Adrian
911C4

Randall G.

Yes, you gotta' have the Bosch Hammer, because the fault is stored in nonvolatile memory, and the hammer can "talk" to the control unit. You can do all the unplugging (of the clock) and disconnecting/reconnecting (of the battery, relay, etc.) you want, and those lights aren't going away. For non-computer types, nonvolatile memory is memory that does not reset on a loss of power.

Agreed ... even though I fixed a reoccurring airbag warning light by replacing the clock two years ago.

Unfortunately, before the dealer replaced my clock, I twice had the light reset (by my independent mechanic) with no error codes found--which cost me $120 in "hammer time" .

Bill Gregory

Did you get to keep the socket as a souvenir?