TechTips

Practicing "Safe-jump" Procedures

Late-model Cars Sensitive To Electrical Surges
by Jim Watson

In a few short weeks it’ll be time to fire up that starting unit in the back of your tow truck. That’s right, you’re just weeks away from subzero temperatures and the joys of cold wind nipping at the back of your neck. To warm your heart, think about all the starters, alternators and batteries you’ll be selling.

But wait a minute. Will this be the year that you have to dip into your pocket to foot the bill for new PCMs, BCMs and all kinds of fried automotive electronics?

The New-car Generation Needs Some TLC
Late-model cars are getting older and so are their OEM batteries. Unfortunately, these same late-model cars are filled to the brim with solid-state electronics — electronics that are extremely sensitive to electrical spikes.

What does that mean for you? It means you have to change the way you operate your starting service. You and your wrecker operators will have to start practicing "safe-jump" procedures.

For example, if your starting unit is capable of operating at 18 or 24 volts, forget that it even came with that option. Jump-starting with anything more than 17 volts can turn a PCM into a smoldering mass of solder and deep-fried chips. And, if you think the customer isn’t going to come after you for the cost, think again! Be prepared to hear the customer say, "The car ran fine before you jumped it."

These cars need TLC when jump-starting. First, turn down the voltage on your starting unit. Disable the 18 or 24 volt setting so you aren’t tempted to "get this over with quicker" while your toes freeze off. Tape over the settings with duct tape. Fifty or 60 layers should do it.

Second, make sure your wrecker has a battery tester on board and use it before deciding to fire up the starting unit. Remember, when battery voltage falls below 9.5 volts, most PCMs go into shut down mode. You must first bring the battery up to operating voltage before you are going to see any signs of life from the PCM.

Third, because of the minimum battery voltage issue, you need to resign yourself to the fact that you are going to be doing more battery charging with your starting unit and fewer "power blasting" jump-starts. Figure this into your pricing structure. Allow yourself at least 5 minutes battery charging time (preferably 10 minutes) with your starting unit set at a reasonable voltage level, before having the customer turn the key.

Fourth, turn off all automotive accessories before charging or jump starting! This warning even applies to radios and cell phones! Why put yourself at risk of blowing out a $450 radio for the $25 you charge for a jump-start?

Fifth, make sure your starting unit is shut down completely before disconnecting the cables. Just like your desktop computer, your goal is to avoid surges. Disconnecting the cable with current flowing is a sure-fire way to generate a surge. Disconnect the negative cable first.

Also, remember that when the car failed to start, the customer probably attempted to give it "a little more gas" before they called you. That extra gas has most likely fouled the plugs, making for extended cranking even with a jump. Be sure to warn the customer that they may be better off being towed to the shop for new plugs and an oil change, rather than a new starter and new plugs and an oil change.

"It’s your fault my car runs bad" When the PCM loses keep-alive power, you should expect driveability problems. That’s why it is so important to test battery voltage as soon as you arrive at the customer’s car. If the battery shows below 9.5 volts, explain to the customer up-front that their computer may have lost its adaptive and idle learn memory, and that you may have to put the car through a relearn procedure — for an extra fee. Get their approval before you do the jump.

For example: GM TSB 89-41-6E explains the IACV relearn procedure for the 2.8L V-6 engine. The PCM loses its idle air control valve position setting when it loses battery power.

Note that this is at least a 15-minute procedure — in addition to the time you spend on the jump. Yet, it ensures that your customer will have a decent idle quality once they drive away from the jump-start. You do not want to risk being blamed for driveability issues, nor do you want to give away your time for performing relearn procedures.

The Plot Thickens
If driveability relearn procedures weren’t bad enough, there are many other relearn procedures for body computers and accessory electronics. There’s even one for resetting a power sliding door on a GM vehicle after losing battery power (GM TSB 53-81-15A).

Once again, remember to advise customers up-front that their power sliding door may not operate properly unless it is reset. Don’t open yourself up to charges of damaging their power sliding door.

The story doesn’t end there. Many theft deterrent radios, security systems, cell phones, etc., need to be put through a relearn procedure. This isn’t limited to GM cars, either.

Whether you see jump-starting as a necessary evil or an excellent way to make big dollars in a short period of time, you must pay attention to the dangers present in jump-starting today’s computerized cars. One fried PCM can kill your profits for the whole day.

In addition to avoiding the dangers of jump starts, you must also educate yourself on the additional fee-generating opportunities for resetting automotive electronics. Print up a price list for these services and present it to the customer while you are performing your battery tests. When it’s 30 degrees below zero, customers will gladly pay you to get the power door to slide, the engine to idle properly and the radio to work. At 30 degrees below zero, even I would pay you to crawl under my dash to pull a fuse — a sure sign that I’m getting old.

Jim Watson is the team leader for the GM section of AutoLine Telediagnosis. He has 17 years experience as a technician and holds both a master and L-1 certification. In 1989, Watson received the NTDRA-ASE Master Tech of the Year award.

Each month, technicians from AutoLine Telediagnosis (http://www.autoshop-online.com) share valuable TechTips with our readers. As an ASA member, you’re already signed up to use the AutoLine technical diagnostic service at a discounted rate.

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AutoInc. Magazine ®, Vol. XLIV No. 11, November 1996