Elec­tronic Di­ag­nos­tics: Mazda6 2.0 petrol

Trac­ing and fix­ing faults in elec­tronic en­gine man­age­ment sys­tems

Car Mechanics (UK) - - Contents -

Well re­ceived by the pub­lic and the press for its per­for­mance and prac­ti­cal­ity, the Mazda6 also has a good rep­u­ta­tion for re­li­a­bil­ity.

Kim Hen­son and Ed­ward Hag­gar in­ves­ti­gate whether this ex­tends to its di­ag­nos­tic as­pects.

The first-gen­er­a­tion Mazda6, des­ig­nated GG1 and es­sen­tially de­rived from the 626, made its in­ter­na­tional de­but in 2002. This well-re­spected model was sold in four-door sa­loon, five-door hatch­back and five-door es­tate forms, and with a va­ri­ety of en­gine/trans­mis­sion op­tions. Sec­ond-gen­er­a­tion mod­els ar­rived in 2007, launched at that year’s Frank­furt Mo­tor Show and built on Mazda’s GH chas­sis. As with other Maz­das, the car has many de­sign/com­po­nent links with con­tem­po­rary Fords.

The sec­ond-gen­er­a­tion cars were sold in four-door sa­loon, five-door hatch­back and es­tate ver­sions and were widely praised for their dy­namic qual­i­ties, as well as prac­ti­cal­ity for fam­ily use. En­gine choices were 1.8-, 2.0- and 2.5-litre petrol units, plus a 2.0-litre diesel (a 2.2-litre joined the line-up from 2009).

A facelift in 2010 re­sulted in frontal restyling and in­te­rior up­grades. Th­ese cars were well-equipped and make good sec­ond­hand buys to­day. The third­gen­er­a­tion GJ was avail­able from 2012.

Our ve­hi­cle for this fea­ture is one of the sec­ond-gen­er­a­tion 2.0-litre four­cylin­der mod­els, dat­ing from Septem­ber 2009. Guid­ing us through this petrol en­gine is Ed­ward Hag­gar.


Com­pared to other modern cars, ac­cess around the Mazda6 en­gine is very good. Be­fore car­ry­ing out any di­ag­nos­tic work, it is worth check­ing the ser­vice his­tory of the ve­hi­cle and tak­ing a close look at the aux­il­iary drive­belt. If the belt is show­ing signs of a line on its ex­ter­nal sur­face and is turn­ing brown in colour, it is on bor­rowed time, so re­new it as soon as pos­si­ble.

Note that this en­gine in­cor­po­rates a tim­ing chain, rather than a belt, but prob­lems can arise if reg­u­lar oil and fil­ter changes are not car­ried out. Re­new both ev­ery 6000 miles or six months, whichever comes first, to guard against fu­ture trou­ble.

Fault 1


With our first fault on this Mazda6, the en­gine may be run­ning in ‘limp-home’ mode, with the en­gine mal­func­tion lamp on the dash il­lu­mi­nated. Fault codes ‘P0140’, ‘P0571’, ‘P0600’ and ‘P2101’ may be stored, re­lat­ing to a faulty bat­tery or low volt­age.

Recharg­ing the bat­tery may re­store nor­mal run­ning, af­ter which the stored fault codes need to be cleared, but the prob­lem will re­cur if the bat­tery or charg­ing sys­tem is weak and the volt­age level falls again. In this case, the charg­ing sys­tem will need to be re­paired and/or a new bat­tery fit­ted.

Fault 2


Our sec­ond fault with this Mazda man­i­fests it­self in the form of oc­ca­sional non-start­ing. This may be due to cor­ro­sion or dirt ad­versely af­fect­ing the earth con­nec­tion on the left-hand sus­pen­sion tur­ret. Of­ten, if you hold the ca­ble and move it from side to side, the en­gine will then start.

Dis­man­tling the joint, care­fully clean­ing all con­tact faces and re­assem­bling the earth con­nec­tion com­po­nents, us­ing a sil­i­cone/grease prod­uct for fu­ture pro­tec­tion, will usu­ally cure the trou­ble. How­ever, if the cor­ro­sion is se­vere, it may be nec­es­sary to re­new the earth ca­ble/con­nec­tor.

For own­ers, it’s heart­en­ing to know that Maz­das, and Ja­panese cars in gen­eral, are usu­ally pretty good elec­tri­cally-speak­ing.


If en­gine oil and fil­ter changes are ig­nored, even­tu­ally the tim­ing chain ten­sioner will be starved of oil, re­sult­ing in the chain be­com­ing slack and jump­ing the sprock­ets. This of­ten oc­curs when try­ing to start the en­gine; if it is al­ready run­ning, it will stop and refuse to restart. The en­gine warn­ing lamp will be il­lu­mi­nated and a fault code in­di­cat­ing a ‘cam sig­nal’ prob­lem will be stored. Don’t be tempted to sim­ply re­new the cam sen­sor, as the un­der­ly­ing fault will still be there.

We ad­vise re­new­ing the en­gine oil and fil­ter at least ev­ery 6000 miles/six months (rather than the 12,500 miles/12 months rec­om­mended by Mazda). With reg­u­lar main­te­nance, th­ese cars can cover well over 100,000 miles with­out prob­lems.

For a fairly com­pe­tent me­chanic, the tim­ing chain is straight­for­ward to re­new, and the re­quired tools are widely and in­ex­pen­sively avail­able.

Fault 4


Our fi­nal com­mon fault is mis­fir­ing/ rough run­ning of the en­gine, ac­com­pa­nied by stored fault codes re­lat­ing to ‘cylin­der misfire’. In this case, the prob­lem is al­most al­ways due to break­age of the tabs that lock the coil con­nec­tor plug to the coil, rather than to a fail­ing coil, as so com­monly oc­curs on other cars. The plug then parts com­pany with the coil and elec­tri­cal con­tact is lost.

We have seen some very poor re­pairs to th­ese con­nec­tors in­volv­ing the use of ca­ble ties and sil­i­cone. While such meth­ods are OK as a tem­po­rary ‘get you home’ mea­sure, a re­place­ment con­nec­tor is cheap to buy and eas­ily fit­ted to en­sure a proper re­pair for re­li­able run­ning.

NOTE: All ref­er­ences in our text and cap­tions to ‘left’ and right’ sides are from the point of view of some­one sit­ting in the car and look­ing ahead.

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