ca993twin

I hope someone can toss out an idea. My car has had a belt tensioner warning light since I've had it. The tensioner was changed. No help. When I looked in my box of old spares, there was another tensioner in there... obviously, this problem has gone on for quite awhile. I've just changed the wire harness because I was told that it was a broken wire in the harness. I still have the warning light.

I notice that when I put an ohm meter on the two spare tensioners I now own, that the circuit is open until you squeeze the tensioner closed. Then it reads a high value, but only for a short while... then it slowly drops to near (but not quite) zero.

Can there be an issue with the way the tesioner is mounted? Something loose there? It "feels" like the tensioner in the car is "closed", and that should complete the circuit... I think.

Help please.

ca993twin

A little more info that may or may not be useful... the big "I" warning light comes on when I start the car, so I'm pretty sure that this is a real fault, and not a problem in the gauge. In addition, a mechanic tried plugging in a spare clock assembly, and it also showed the belt-tensioner warning.

The more I think about this, the more I think its the way the tensioner is mounted. I just looked again, and now the tensioner feels far from closed (with the engine off)... I can move it a good 1/2 inch or so. This is wrong, isn't it?

Garth S

The switch arm travels and arc of ~1 1/4" - and is closed after the first 1/4". With a normal belt tension, the arm is depressed halfway of the remaining travel ..... leaving ~1/2" to compress the roller against the switch body. Yours sounds to be in the normal position. It is a simple on/off micro switch located by a couple of plastic lugs on the backside and an allan bolt.
It can only read <1 ohm (closed) or infinite ohms (open) - if the reading changes with time, check the battery in the meter.

nine45s

Steve,

As I just had mine off for a squeak problem I can tell you I could move it about a 1/2 inch off the belt. I have no light problem.
Pull the connector off the one that is mounted on your car and check it with your meter, if it shows open you do have a mounting problem.

Gerry

BobbyT

Hi Steve,

Take a close look at the underside of the moveable arm that the roller is mounted on. Mine was cracked, which might cause an erroneous reading.

Also, with the sensor installed, and the key on (engine not running, of course), does the warning light go out if you push the wheel away from the belt?

ca993twin

Thanks all for the suggestions. BobbyT... I was just about to ask if you get a valid reading with the key on, but engine off. If so, then all of you probably never, ever see this light, even with the engine off... is this true?

BobbyT

All the warning lights should illuminate at the key "on" position, before the engine is started, as a bulb test.

BobbyT

BTW, this really isn't a tensioner, just a sensor to warn if the cooling fan belt breaks. This wasn't required on older 911s which had only one belt driving the alternator and the fan, because if that belt broke, you would get a warning light via the charging system when the alternator stopped turning.

ca993twin

Bobby,

OK.. I'm a doofus, and I'm confused. Your first post said try to manually move the tensioner with the key on, but engine off to see if the light goes out. Your last post says that all of the lights are on with key on, engine off as a bulb test. This sounds contradictory, yet if it can work, a great avenue for debug. My light to seems to be always on, no matter what I do with that tensioner. Thnaks for your continuing help.

Droops83

I'll bet that you have an open in the wire(s) that runs from the warning light to the sensor. If I remember correctly, belt tension against the sensor arm makes it contact the microswitch inside, thus completing the circuit and keeping the light off. If the belt breaks or loses tension, the arm pops out and away from the switch, opening the circuit and turning the light on. The fact that you have had the sensor itself replaced several times and you said a mechanic try a different gauge seems to point to an open. Get an ohmmeter and a real long set of leads and check for continuity in the wires that run between the gauge and the sensor. If I have time at work tomorrow I will check the factory wiring diagram for the wire colors and any more details about this circuit . . . .

---

Chris Andropoulos
Schneider Autohaus
Santa Barbara, CA

BobbyT

Sorry, Steve--my bad. You might be able to test it by pushing back on the roller arm if you started the engine and then stalled it, with the key left on...

ca993twin

Thanks guys.

Chris, we've just replaced the main engine wire harness as well, on the assumption it was a broken wire in there someplace. Grrrrr.

Droops83

Steve,

I took a really quick look at the factory wiring diagram today . . . as i suspected the signal wire from the sensor runs to a control module and then another wire runs from there to the light in the clock. Both wires are green/brown. I did not have time today to take a close look at the 993tt we have right now it was so damn busy, but I know the body control module is on the front "firewall" in the luggage compartment, under the cowling, and on the 993tt it looks like it's buried under some stuff. I am going to be yanking the engine out of this car tomorrow if I have time, so I will take a closer look at where this control module is. Also there are two connectors between the sensor and the module that are back in the engine compartment, make sure those are secure and clean.

If you feel like doing some detective work, pull off the front cowling and locate the BCM. It should have a 20+ pin wire harness connected to it. Find both green/brown wires, those are the ones for the belt sensor. Check for continuity between the wire end at the gauge and the other end at the harness, and get a really long set of leads (connect a few together if you have to) and check for continuity between the other green/brown wire in the harness at the other end of it at the belt tension sensor connector. If you have continuity in both wires and the light is still on, i'd hit up one of your 993 buddies and plug in another body control module and see if it goes out. Hope this helps, I will take a closer look at this tomorrow on the car we have and let you know exactly which wire is which.

---

Chris Andropoulos
Schneider Autohaus
Santa Barbara, CA

ca993twin

Chris,

Dang... now I'm kinda wishing I had brought my car to your shop! Body Control Module? Who woulda thunk it? Thanks for spending the time to help with the diagnosis.

Droops83

Steve,

Glad to help, you have an awesome car and I hope this works out . . . I was wondering, several months ago I was driving on 101S in Santa Barbara on my way home and saw a line of badass 993s, and a couple seemed to be Rufs, I think one was Arena Red couldve been yours and another was a black BTR. You guys exited at Cabrillo and I think I may have inadvertantly cut one of you guys off trying to see where you were going (I was in dark blue Toyota Celica), and if you were gonna stop, but you guys turned around under the freeway and got back onto the northbound onramp, and the lead guys pulled over on the shoulder and waved me by. It was a bummer since I was hoping you guys were gonna stop in a parking lot somewhere! Anyway I'll look at the poor sick Andial 3.8tt we have when I get a chance this week and give you more details . . .

--Chris