Relays

 

Complexity is both the salvation and bane of the car industry.

Modern cars contain somewhere between 30 and 50 'computers' (or 'processing elements') which are responsible for maintaining the operation of the onboard systems. These include systems which constantly monitor the engine to ensure it is operating at peak efficiency (to make sure it isn't wasting gas or polluting the air), systems which constantly monitor the tires and suspension and brake systems (to ensure it has a good grip on the road and is ready to respond to emergency situations should they arise), and systems which control the onboard entertainment (to keep the passengers from getting bored). 

In the case of the 2001 Toyota Corolla, one of those systems controlled the lights (head, tail, running) to make sure they operated according to a strict set of rules: for example, lights would turn themselves off after a certain amount of time if the car was not turned on. This is a fantastic feature which helps avoid that most horrible of circumstances when one discovers that the battery has gone flat because one or more of the lights (internal or external) were inadvertently left on overnight.

In order to facilitate this wonderful feature, and move the car along the path of advancing technology, it was decided to consolidate a host of light-control features into a single module, known as the Relay Assembly / Running Light module, thus replacing a number of mechanical relays with a small plug-in package.

For the better part of its lifetime, at least for the Corolla in our possession, this module has worked flawlessly.

But a recent incident revealed a somewhat dubious design issue.

Somewhere in the bowels of the module, an element failed. As a consequence of this failure, the light controller no longer worked properly; in fact, the module began to operate in direct contradiction to the Prime Directive: even with the car off and the key removed, the lights remained on and they could not be turned off without disconnecting the battery.

In the Aerospace Industry, we have what is known as Failure Modes; and it is imperative that every possible Failure Mode is determined and evaluated and designed such that the Aerospace Prime Directive ("No human shall come to harm") is not violated.

It is obvious that not all the Failure Modes of this module were adequately evaluated to ensure that the Battery Conservation Prime Directive was upheld. The module failed. The lights stayed on.  

 And the battery died.

Ordinarily, the death of a battery is not a critical issue, especially if the battery is not so much dead as it is insufficiently charged to support starting the car. In that case, it is a simple matter to jump-start the car using a set of battery cables and a convenient secondary vehicle. However, in this particular case, though valiant efforts were made, the attempt was unsuccessful. A complete battery replacement was necessary. For somewhere in the neighborhood of $100.

Afterward, an analysis of the failure revealed the culprit to be the Relay Assembly; a new assembly was located on-line. From OEM suppliers, a new part was priced around $250; on eBay, the same part (used) was $40.

Guess which one I ordered?

The new (used) module worked like a champ for about 4 weeks. 28 days. The seller guaranteed it for 30 days. Guess what happened on day 28?

Yep. It failed. And it failed in a much more spectacular way than its predecessor. Instead of just not working, it decided to give off the distinct aroma of burning electronics while failing! What fun! Nothing better than smelling a potential fire inside the car while driving down the road.

Luckily, the driver made it home safely. At which point I pulled the new (used) module from under the passenger dashboard, took a deep, refreshing whiff of the burnt element, and retreated to the office to send a message to the seller to find out how this guarantee thing worked.

The seller was willing to provide me with a replacement unit, but with one little caveat: he insisted that I measure the output of the alternator to verify that it was not too high. He also insisted that the Relay modules were very sensitive to over-voltage and he couldn't guarantee them if my alternator was putting out too much. What's too much? I asked. He didn't want to tell me until I had measured and reported the alternator voltage. Because the part couldn't be guaranteed if there was an electrical problem with the car. I got the impression that no matter what voltage I reported, it was going to be too high, according to him.

But I had him ship me the part anyway.

Meanwhile, I took the trouble to look up the standard alternator output on the 2001 Corolla - it is somewhere between 13.7 and 14.7 with all accessories off - so was not surprised to measure approximately 14.6 volts -- with three different voltmeters -- across the battery terminals. 

When the part arrived (finally, after a 2-week delay!), I called up the seller and told him I'd received it, and reported the voltage reading from my alternator output. He claimed that the maximum voltage that the module can take is around 13.6 volts.

So he won't refund my money for the original part.

And I really don't care. I tried to tell him that it doesn't matter to me, that I just want the part so I can get the car on the road again. If it comes down to it, I'll simply design an alternate module using off-the-shelf parts and bypass all the fancy stuff. I'm an electrical engineer; it won't be difficult.

But it annoys me that he didn't even bother to do the same research I did, and provide me a good explanation why a standard OEM part can't handle the standard alternator voltage. According to him.

After all, the first part he sent me lasted for nearly a month. Why would it suddenly go bad?

More importantly, why would Toyota design a part with a stupid Failure Mode?

This is the kind of thing that makes me want to redesign the whole thing anyway, because I know I can do better than that.

Meanwhile, we'll just see how long this new new (used) module lasts.