Electronic Sensors: MTBF
 

Does anyone here have any information about the mean time between failure rates for electronic sensors? I'm sure there must be data on this somewhere. I replaced some recently and began to wonder how often these go bad.

Anybody? I thought maybe one of you MB master technicians would have something to say about this.

I'm not sure that any data exists for "MTBF". . . .

There's data from the manufacturer for "changing" the part b/c its useful life is 'over'. But that's a lot different from MTBF.

For example, a Bosch O2 sensor is recommended for change at 60k miles. But, as we all know, many are still running them well in excess of the mileage.

I'll bet the manufacturer has such information. I suppose it's not to their advantage to share it with us, though. I just replaced one and it got me to thinking.

Of course it depends what type of sensors you are talking about. Some have actual wear such as O2 sensors and MAF sensors and potentiometer type sensors. Others have thermal fatigue such as temperature sensors and CP sensors. But I have no data unfortunately. The experience of a seasoned mechanic would probably be the best indicator.

Mike

The one I replaced was a cam sensor. It turned out to be okay. The harness leading to it had lost some of the insulation and it was probably just shorting out. As long as I had the new part and everything taken apart, I went ahead and replaced it. I hate dealing with electrical problems. . . .

I'm certain that many MB parts are designed to have an expected minimum life-span. I'm also certain that when the failure rate of any given part indicates a problem, MB orders that a failure analysis be carried out, and the MB Quality Evaluation Center (QEC) in Jacksonville, Fla., is given the task of figuring out what the problem is. It's doubtful though, that they'd be interested in sharing that information with the members of this Forum. :D

In my business, MTBF is a ‘sacred’ cow . . . all sub-systems are designed such that the overall system meets or exceeds the MTBF goal. Every system spec calls for a minimum MTBF be met and proven by analysis and then tested to show that it does.

Obviously, ‘cost’ plays a big part of this since it will cost more to design/build the system to meet this goal. If the goal is ‘tough’ to reach, then more ‘reliable’ parts must be used in order to meet the meet the overall system MTBF. So ‘cost’ is a very key element in meeting MTBF but it takes a back seat when the MTBF must be demonstrated.

This system described is a military system. For a commercial system, MTBF is probably treated as secondary since ‘cost’ is the key factor.

I have a favorite: the crankshaft sensor! On early MBs such as my car, it’s a ‘hunk’ of magnetic material wrapped in ‘wire’. A more straightforward device doesn’t exist! How un-reliable can a piece of magnetic material wrapped in wire be??? The MTBF should be through the roof!

In 10+ years at my tech’s shop, I’ve never seen one go bad! How could they unless it gets mechanically damaged; ie the wire breaks or the shield is punctured. Even that is not very probable since it's routed on top of the transmission so it’s not readily accessible to be damaged.

Then MB re-designed this part and made it ‘electronic’ for their newer cars. It’s a small ‘circuit’ then sends a pulse to the control module just as the previous version. Now I’ve seen a lot of them go bad . . . for whatever reasons.

This part must have been designed to lower costs involved and maybe b/c the design of the receiving end of the signal required a higher level? Not sure but to go to an electronic ckt instead of a passive ckt means that the MTBF has to be lower than the former part . . . however the cost must be less otherwise why would it be used.

As a consequence, that small example shows why some of the newer MBs aren’t as reliable as their older counterparts. When you lower MTBF, the product can’t be as reliable!

A failure analysis may show ‘cheap’ parts being used so the only fix is to use better grade of parts b/c you can’t eliminate that part. It must be improved. The consequence is that better parts will increase the overall MTBF as it also increases the cost of the part.

Kinda like chasing your tail!

Whether they share it with us or not, I'm sure most manufacturers have tested this sort of thing. Germans seem even more likely to do so than some other nationalities. Shoot, they kept records of how many people they killed in the concentration camps, how many bullets were used for this and that. They are about as anal as they come. I'm sure THEY know!

Benz does not make electronic sensors, but they might have an MTBF spec that the vendor must meet.