Down­shift­ing can dam­age au­to­matic trans­mis­sion

Winnipeg Free Press - Section E - - AUTOS - JIM KERR

QI have a 2003 Fo­cus with au­to­matic trans­mis­sion. Some­times when I am brak­ing, in­stead of im­me­di­ately ap­ply­ing the brakes, I will shift from drive to 2, then 1. I only use this pro­ce­dure at low speeds be­tween 50 to 70 kilo­me­tres. Will this dam­age my en­gine or trans­mis­sion? Please ad­vice.

AN­SWER: If you shift to a lower gear while at higher speeds, the en­gine could pos­si­bly go above its rpm lim­its, usu­ally called the redline be­cause the face of the ta­chome­ter gauge will typ­i­cally be marked in red at the en­gine r.p.m. lim­its. This can cause en­gine dam­age. How­ever, al­most all au­to­matic trans­mis­sions will not shift to a lower gear even if you man­u­ally se­lect one.

But, any time you shift down man­u­ally, you are plac­ing an ex­tra load on the en­gine and trans­mis­sion. If you are driv­ing in a spir­ited man­ner, you may not care, but if you want to max­i­mize your econ­omy, you are bet­ter to use the brakes to slow the ve­hi­cle and just leave the trans­mis­sion in drive.

There are ex­cep­tions to this. When driv­ing on long down­hill grades, such as you find in the moun­tains, you may wish to shift to a lower gear to help keep ve­hi­cle speeds down, es­pe­cially if you are tow­ing or haul­ing a heavy load. By shift­ing to a lower gear, you are able to use the en­gine com­pres­sion to help brake the ve­hi­cle, and this helps re­duce the pos­si­bil­ity of over­heat­ing the wheel brakes dur­ing a long brake ap­pli­ca­tion.

An­other ex­cep­tion could be when try­ing to stop on glare ice. Shift­ing to neu­tral in some in­stances and us­ing only the brakes to stop the ve­hi­cle will some­times give you bet­ter ve­hi­cle con­trol dur­ing stop­ping, be­cause the en­gine has no ef­fect on the drive wheels. Be pre­pared to shift back to drive if you need to drive your ve­hi­cle away from a po­ten­tial col­li­sion.

When you man­u­ally se­lect a lower gear in an au­to­matic trans­mis­sion, you are in­creas­ing trans­mis­sion hy­draulic pres­sures and of­ten ap­ply­ing ad­di­tional clutch packs. This min­i­mally in­creases wear in the trans­mis­sion if done oc­ca­sion­ally, but if done all the time, it will wear out the trans­mis­sion faster. Re­pair­ing brakes is cheaper than re­pair­ing trans­mis­sions, so I sug­gest us­ing the brakes, un­less you need the per­for­mance of a lower gear.

Q: I have a 2003 Pon­tiac Sun­fire. I lost all the gauges in the dash, such as speedometer, gas, r.p.m. and tem­per­a­ture. This seemed to hap­pen when the bat­tery went dead. It was jump- started. Would that cause the gauges to quit work­ing? Is there any­thing I could check be­fore tak­ing a lot of things off or apart? Could it be the ground wires or fuses?

A: The in­stru­ment panel clus­ter (IPC) is ac­tu­ally a com­puter mod­ule. The four gauges you have in­di­cated and some of the warn­ing lights are op­er­ated by the IPC us­ing in­for­ma­tion they get from the body con­trol mod­ule (BCM) and the en­gine con­trol mod­ule (ECM). It is pos­si­ble the data line be­tween th­ese mod­ules and the IPC is bro­ken, but it is wired in a “loop” sys­tem, much like an old tele­phone party line (so all the mod­ules can lis­ten to the data con­ver­sa­tion), and it would take two breaks in the loop be­fore data com­mu­ni­ca­tion to the IPC would be lost.

The fastest way to ver­ify if IPC is get­ting data is by us­ing a scan tool to com­mu­ni­cate with the IPC. Be­fore do­ing that, you should check the fuses for the IPC. There are two fuses in the fuse box in­side the left end of the in­stru­ment panel. Re­move the cover and look for the 10-amp clus­ter fuse and the 10-amp BCM/CLU fuse. Re­move th­ese two fuses and in­spect them for opens. If they are good, re­in­stall them af­ter about one minute. This al­lows the com­puter mod­ule to power down and re­boot.

If the other warn­ing lights are work­ing, the IPC ground should be good, but you could check Ground G110, which is bolted to the top of the trans­mis­sion mount­ing bolt on the en­gine. If the power, ground and data com­mu­ni­ca­tion are good, then the prob­lem is with the IPC. A volt­age surge dur­ing the boost­ing can dam­age com­puter com­po­nents, and you may have to re­place the IPC.

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