Di­ag­nos­tics Mas­ter­class

Learn the skill of read­ing and in­ter­pret­ing ve­hi­cle elec­tron­ics.

Car Mechanics (UK) - - Contents -

One of the most fre­quent com­ments we hear from CM read­ers is that mod­ern cars have be­come so re­liant on elec­tron­ics that it’s be­com­ing vir­tu­ally im­pos­si­ble for home me­chan­ics to work on them with­out spend­ing a small for­tune on di­ag­nos­tics equip­ment. How­ever, a suit­able di­ag­nos­tics de­vice needn’t cost the earth and a ba­sic abil­ity to read – and, more im­por­tantly, in­ter­pret – fault codes can be learned by any­one. It’s a skill that’s es­sen­tial for every 21st cen­tury mo­torist to un­der­stand how their car is per­form­ing, as well as what is go­ing wrong.

Think­ing out­side the box

While much of this fea­ture fo­cuses on di­ag­nos­tic equip­ment, a good home me­chanic must never make the mis­take of think­ing that iden­ti­fy­ing faults and mak­ing re­pairs to mod­ern ve­hi­cles can be per­formed solely us­ing an offthe-shelf di­ag­nos­tic de­vice. Even the pro­fes­sional mo­tor trade is strug­gling to change pub­lic per­cep­tion about the process of au­to­mo­tive prob­lem-solv­ing, be­cause many of their clients be­lieve that a quick (and, they as­sume, cheap) plug-in cure is all that is nec­es­sary to re­solve a fault, in­clud­ing ex­tin­guish­ing a trou­ble­some en­gine man­age­ment warn­ing lamp, and this is all that stands be­tween them and an MOT pass.

Di­ag­nos­tics is a com­plex prob­lem­solv­ing process that en­tails in­vest­ment in not only hard­ware and soft­ware, but also train­ing and ex­pe­ri­ence. With in­creas­ing num­bers of peo­ple turn­ing to both garages and DIY di­ag­nos­tic equip­ment sup­pli­ers in the hope that ‘the box’ alone will solve their prob­lem, it can be ar­gued that they are caught in a distress pur­chase loop. Try to keep a level head and do not al­low your judge­ment to be clouded by the press­ing need to get back on the road as quickly as you can.

Through­out his many years of train­ing pro­fes­sional me­chan­ics, Neil Hil­ton of Hella Gut­mann So­lu­tions told us that the sin­gle big­gest mis­take he en­coun­ters is an over-re­liance on fault codes. This might be be­cause it is hu­man na­ture to take the eas­i­est op­tion. Di­ag­nos­tics can­not be about a ma­chine alone, be­cause hu­man thought pro­cesses are in­te­gral to the prob­lem-solv­ing process, which in­cludes eval­u­at­ing crit­i­cally the in­for­ma­tion that is pre­sented (in­clud­ing that from a di­ag­nos­tics ma­chine – this in­cludes fault codes) and com­ing to a log­i­cal con­clu­sion. This is where skill and ex­pe­ri­ence re­main as rel­e­vant as ever and is how pro­fes­sional work­shops jus­tify their charges. It is no co­in­ci­dence that ‘di­ag­no­sis’ is de­rived from the Greek word mean­ing ‘know­ing thor­oughly’ – you have to eval­u­ate the symp­toms to ar­rive at a log­i­cal root cause of the prob­lem, gath­er­ing in­for­ma­tion from dif­fer­ent sources and use your eyes and ears to sense if any­thing is un­usual, rather than sim­ply tak­ing fault codes as gospel.

In­ter­pret­ing & deal­ing with fault codes

Un­like a tra­di­tional oil pres­sure warn­ing light that re­lies on a fairly sim­ple elec­tri­cal cir­cuit to in­di­cate one spe­cific fault, other fas­cia warn­ing lamps can re­late to a num­ber of is­sues that have been logged by an ECU. Notably, these in­clude the en­gine man­age­ment

warn­ing lamp (known oth­er­wise as a mal­func­tion in­di­ca­tor light or MIL), Abs/trac­tion con­trol and SRS (airbags). As the faults can­not be pin­pointed to a sin­gle is­sue, the rel­e­vant com­puter needs to be in­ter­ro­gated for a fault code, which could help to nar­row the prob­lem to a par­tic­u­lar com­po­nent in a cir­cuit, such as a sen­sor. It may be worth try­ing to re­set the code be­fore in­ves­ti­gat­ing fur­ther. Should the re­set fail, or the same fault code reap­pear af­ter a short time, then it is un­likely that the fault gen­er­ated is a ‘ghost’ code, which may have been trig­gered by some­thing else, such as elec­tro­mag­netic in­ter­fer­ence, or a sud­den dip in volt­age, which might have been caused by an ail­ing bat­tery.

While the ECU ob­tains data from a num­ber of in­for­ma­tion sources, not all of them are ac­cu­rate. For ex­am­ple, the en­gine ECU might iden­tify a Lambda sen­sor as faulty, due to ex­ces­sive ex­haust emis­sions not be­ing re­duced suc­cess­fully by ad­just­ing the fu­elling, when the real cause is a leaky fuel in­jec­tor, the so­le­noid of which is re­turn­ing sig­nals to the ECU that are within tol­er­ance.

Bear in mind that even mod­ern en­gines do not have sen­sors that mon­i­tor crank­shaft, fly­wheel or pis­ton con­di­tions. Fur­ther lim­it­ing fac­tors in­clude uni­ver­sal fault codes be­ing re­stricted in num­ber, as well as a need to con­sider that the code it­self might not in­di­cate a prob­lem with a com­po­nent, but rather the cir­cuit that the ECU as­so­ci­ates with it – the wiring, con­nec­tor plugs and even other as­so­ci­ated com­po­nents up­stream could be to blame for send­ing false sig­nals.

This in­cludes bad earths, which can trig­ger a plethora of codes. Check the ba­sics, such as in­spect­ing earth leads for cor­ro­sion and eval­u­at­ing the bat­tery and al­ter­na­tor per­for­mance, be­fore re­plac­ing com­po­nents blindly.

Thijs Jasink of Ac­tron­ics, a com­pany that re­man­u­fac­tures elec­tronic com­po­nents, told CM that 30-35% of the parts that it re­ceives have noth­ing wrong with them, es­pe­cially ECUS. Most com­monly, the me­chanic has mis­di­ag­nosed the com­po­nent as be­ing the fault. How­ever, spe­cial­ists such as Ac­tron­ics, are worth con­tact­ing for ad­vice, be­cause they can ei­ther in­ter­ro­gate the ECU in more depth for you, or else of­fer ad­vice about any other com­po­nent that may be in­flu­enc­ing the ECU in a cer­tain way.

Con­sider also that fault codes can be tem­po­rary, in­di­cat­ing the pres­ence of an in­ter­mit­tent prob­lem. In cer­tain cases, should the rel­e­vant ECU de­tect that the anom­aly is not present any longer, it may ex­tin­guish the warn­ing light but the fault code may still be logged in the sys­tem. If the lamp, es­pe­cially the MIL, has been lit for a fairly long pe­riod of time, sev­eral com­po­nents may be re­spon­si­ble. Ad­dress­ing one fault may not present a so­lu­tion, be­cause you have freed-up a longer list of multi-lay­ered prob­lems that the orig­i­nal is­sue may have masked. This is why it’s es­sen­tial to ad­dress any warn­ing lamp as soon as pos­si­ble.

When ser­vic­ing the ve­hi­cle your­self, you may un­cover a list of fault codes that are not se­ri­ous enough to war­rant il­lu­mi­nat­ing a fas­cia-mounted warn­ing lamp. These can range from codes in­volv­ing the body con­trol com­puter to the cli­mate con­trol sys­tem. Should you sus­pect that they have been present for a long time, some di­ag­nos­tic de­vices will per­mit you to check not only if they are per­ma­nent, or in­ter­mit­tent, but also the fre­quency wth which they ap­pear.

Pro­gram­ming & cod­ing

In the past, you could re­set an en­gine man­age­ment, ABS, or even SRS ECU by dis­con­nect­ing the bat­tery for sev­eral min­utes. Mod­ern ve­hi­cles are more so­phis­ti­cated. Many mod­els have spe­cific bat­tery dis­con­nec­tion/ re­con­nec­tion pro­ce­dures that must be fol­lowed to avoid dam­ag­ing their del­i­cate elec­tron­ics. When a ma­jor re­pair has

been com­pleted, re­cal­i­bra­tion of cer­tain en­gine func­tions might be re­quired. For ex­am­ple, di­rect-in­jec­tion petrol en­gines can suf­fer from their in­take tracts be­com­ing clogged with rub­bery car­bon that re­stricts air­flow. Be­ing a grad­ual process, the ECU re­learns and adapts ac­cord­ingly with­out il­lu­mi­nat­ing the MIL, or log­ging a fault code, pro­vided that the con­di­tions re­main within tol­er­ance. How­ever, when the in­let is cleaned, the sud­den dif­fer­ence might con­fuse the ECU, hence why ei­ther re­set­ting or re­cal­i­bra­tion is nec­es­sary.

While di­ag­nos­tic tools are needed to code cer­tain new/re­man­u­fac­tured re­place­ment parts to your car, such as ECUS and fuel in­jec­tors, the tool might be needed for cer­tain ser­vice pro­ce­dures. On some Mercedes-benz mod­els, for ex­am­ple, the sim­ple DIY task of re­plac­ing the air fil­ter dic­tates that the ECU needs re­cal­i­brat­ing to take into ac­count the sud­den change in air­flow char­ac­ter­is­tics. Not re­set­ting ei­ther the ser­vice/oil qual­ity in­ter­vals di­ag­nos­ti­cally can make many mod­els as­sume that a ser­vice has not taken place. This can re­duce ac­tive diesel par­tic­u­late fil­ter re­gen­er­a­tion rates, for ex­am­ple, and in­crease the risk of ei­ther fil­ter, or tur­bocharger dam­age.

Ad­di­tion­ally, re­plac­ing the smaller and lighter bat­ter­ies on many mod­ern cars that pos­sess smart charg­ing sys­tems re­quires the new bat­tery to be reg­is­tered and pro­grammed to the car, which re­sets the charg­ing al­go­rithms within the mon­i­tor­ing soft­ware to en­sure that the fresh bat­tery is charged ad­e­quately. The di­ag­nos­tics pro­ce­dure should re­move any low bat­tery warn­ings as well. Fail­ure to do this will af­fect the op­er­a­tion of other sys­tems, such as the stop-start func­tion.

Which di­ag­nos­tic tool to choose

No clear def­i­ni­tion ex­ists be­tween an after­mar­ket code reader, a scanner, or a di­ag­nos­tic tool, so take mar­ket­ing claims with a pinch of salt when con­sid­er­ing the huge range of de­vices avail­able.

In­ex­pen­sive fault code read­ers have been around for many years and can ac­cess generic fault codes within the en­gine man­age­ment ECU. How­ever, the least ex­pen­sive types may not be able to pro­vide you with man­u­fac­turer spe­cific codes, let alone pro­vide any fur­ther di­ag­nos­tic in­for­ma­tion. The very cheap­est tools will not nec­es­sar­ily be able to ac­cess the ECU for every make of car, pro­vide you with live data read­ings, or per­form ac­tu­a­tion tests and pro­gram­ming func­tions. You should also en­sure that the equip­ment can save or print any live data read­ings, so that you can com­pare them. If your bud­get will stretch to it, in­vest­ing in equip­ment that will pro­vide ad­di­tional data, such as wiring in­for­ma­tion, will give you a bet­ter chance of pin­point­ing and iden­ti­fy­ing the fault, with­out re­plac­ing parts that are in good or­der.

Con­sider your needs, too. Your choice of de­vice will de­pend on whether ded­i­cated di­ag­nos­tics are needed for just one car, or whether you look af­ter a num­ber of dif­fer­ent ve­hi­cles in your house­hold and/or like to change your car reg­u­larly. You can buy ‘cracked’ ver­sions of the car-maker’s own soft­ware from var­i­ous sources for a one-off fee, but these tend to work only if you favour a cer­tain make. While you should be able to con­duct most of the ser­vices sup­plied by main dealer di­ag­nos­tic de­vices, pro­gram­ming/cod­ing may be lim­ited, as are cer­tain up­dates, be­cause your ‘pi­rated’ soft­ware might not be able to ac­cess the maker’s server.

A num­ber of di­ag­nos­tic de­vice sup­pli­ers are spe­cial­is­ing in cer­tain makes to pro­vide more in-depth func­tions. Carly, for ex­am­ple, has both free and pro­fes­sional (cost­ing £43.99)

apps for each of the ma­jor Ger­man man­u­fac­tur­ers and for Re­nault, which is used via a VCI (cost­ing £44.90) that sends the in­for­ma­tion via Blue­tooth from the EOBD socket to your mo­bile phone, or lap­top. It can read and com­pare mileages be­tween ECUS and alerts you of any dis­crep­ancy that might in­di­cate odome­ter fraud. Make-spe­cific di­ag­nos­tics can also per­mit you to make ad­vanced ad­just­ments, such as cruise con­trol tol­er­ances (which can have a pos­i­tive ef­fect on fuel con­sump­tion), and change in­te­rior light­ing/warn­ing noise char­ac­ter­is­tics.

In­ves­ti­gate if any sub­scrip­tion/up­date fees are charged, too. The Neb­ula Mech 5, for ex­am­ple, cov­ers mul­ti­ple mod­els but, aside from the £150 cost for the VCI, it op­er­ates via a cloud-based sys­tem that re­quires a £29 an­nual sub­scrip­tion fee (of which the first month is free) to ac­cess up­dates. How­ever, you pay only when you use it and the re­tailer that we con­tacted, Hick­leys, told us that it works to the same level as a pro­fes­sional tool cost­ing be­tween £2000-£3000 and will con­duct fuel in­jec­tor cod­ing as well.

Generic hand-held code read­ers are of­fered by sev­eral re­spected tool com­pa­nies, but their out­right pur­chase prices can be quite high, al­though you can bal­ance this against the fea­tures, make/mod­els cov­ered, as well as the cost and avail­abil­ity of up­dates.

Should you own a car from a Ja­panese, Chi­nese or Korean man­u­fac­turer, note that some generic sys­tems might not of­fer the best sup­port for those mod­els and the ven­dor should be ques­tioned care­fully. De­cide on your pre­ferred in­ter­face – would you pre­fer lap­top/tablet/mo­bile, for ex­am­ple – and do you need your VCI to be Blue­tooth-com­pat­i­ble?

Un­less you can be sure that the buyer is rep­utable and prefer­ably Uk/eu­rope­based, we do not rec­om­mend buy­ing di­ag­nos­tic equip­ment through on­line mar­ket­places such as ebay or Gumtree. The lure of a bar­gain might tempt you, but the level of tech­ni­cal sup­port must be ques­tioned, as well as the avail­abil­ity of up­dates and the risks as­so­ci­ated with plug­ging a VCI of un­known ori­gin into a rel­a­tively ex­pen­sive ve­hi­cle.

Ad­vanced di­ag­nos­tics – ADAS cal­i­bra­tion

Di­ag­nos­tic ba­sics were cov­ered in depth in the June 2017 is­sue of CM. How­ever, the in­creas­ing (and of­ten manda­tory) use of Ad­vanced Driver As­sis­tance Sys­tems (ADAS), es­pe­cially in the last five years, means that more in-depth di­ag­nos­tic cal­i­bra­tion is be­com­ing an in­creas­ingly rel­e­vant post-re­pair safety is­sue.

From a DIY per­spec­tive, the si­t­u­a­tion is worth con­sid­er­ing, be­cause many early Adas-equipped cars have en­tered the sec­ond­hand mar­ket and may no longer be un­der war­ranty. The lat­est ADAS safety func­tions, which in­clude road sign recog­ni­tion, auto-park­ing, adap­tive LED ma­trix light­ing and pedes­trian de­tec­tion, rely on sen­sors, cam­eras and long- and medium-range radars that are po­si­tioned within the struc­ture of the doors, be­hind the front grille and on the bumper cor­ners, not just within the wind­screen. Many of these re­quire in­di­vid­ual cal­i­bra­tion. For the lat­est mod­els, post-re­pair cal­i­bra­tion will add to re­pair costs sig­nif­i­cantly, un­til such a time ar­rives when self-cor­rect­ing sys­tems are de­vel­oped. For now, how­ever, many older Adas-equipped cars fea­ture a wind­screen-mounted cam­era, which is why the cal­i­bra­tion of this sys­tem alone is our fo­cus.

Front screen-mounted sen­sors have been around for more than a decade, of­fer­ing auto-light­ing and wind­screen wiper ac­ti­va­tion. These are be­ing re­placed by cam­eras and long-range lasers that of­fer safety func­tions to in­flu­ence the brakes, en­gine and even the steer­ing. Should they not be cal­i­brated cor­rectly, the car may not re­act safely to a po­ten­tial haz­ard. For ex­am­ple, a mis­align­ment of a wind­screen cam­era by one de­gree can cause an in­ac­cu­racy of up to seven me­tres.

Hella Gut­mann So­lu­tions has been pro­vid­ing ADAS main­te­nance and cal­i­bra­tion ser­vices out­side the main dealer net­works for five years. Its head of busi­ness devel­op­ment Neil Hil­ton told

Car Me­chan­ics: “In­ca­pable di­ag­nos­tic tools, lack of knowl­edge, ex­per­tise and train­ing, tied with un­suit­able pro­cesses, are prov­ing to be real headaches with main­tain­ing the cal­i­bra­tion of these crit­i­cal safety sys­tems.”

It is not al­ways straight­for­ward to know which, or how many, of these sys­tems is in­stalled in a par­tic­u­lar ve­hi­cle. Just as var­i­ous older car mod­els used to have to share the same wiring looms be­tween the ba­sic and top-of-therange ver­sions, cer­tain mod­ern cars are be­ing equipped with the same hard­ware but some trim vari­ants might lack the soft­ware to run them. Should you be able to see ei­ther a sen­sor, or front-mounted cam­era, through a small cav­ity in the top cen­tre of the wind­screen, do not pre­sume that it is op­er­a­tional. Should it be pro­grammed, the sin­gle cam­era might con­trol sev­eral sep­a­rate func­tions. The only way that you can ver­ify a par­tic­u­lar model’s spec­i­fi­ca­tions is to per­form a global scan on your di­ag­nos­tic tool and note which ECUS are com­mu­ni­cat­ing.

The main is­sue sur­round­ing ADAS tech­nolo­gies for a DIYER is that they can stop work­ing, or not op­er­ate cor­rectly fol­low­ing a home re­pair. While a non­func­tion­ing ADAS sys­tem does not cur­rently mean an MOT fail­ure (un­like the MIL, for ex­am­ple), an in­sur­ance com­pany might re­fute a claim if it is found that a faulty driver as­sis­tance sys­tem was a con­trib­u­tory fac­tor in an ac­ci­dent.

Cam­era cal­i­bra­tion

The ma­jor­ity of Adas-equipped cars, made in the last seven years, need re­cal­i­bra­tion af­ter any work has been car­ried out that af­fects the sus­pen­sion ge­om­e­try. Typ­i­cal MOT fail­ure re­pairs that tend to be within a Diyer’s re­mit – such as re­plac­ing a balljoint, sus­pen­sion arm or springs and dampers – will re­quire a di­ag­nos­tic cam­era cal­i­bra­tion af­ter­wards. While many cars that were reg­is­tered within the last five years in­cor­po­rate at least two ADAS sys­tems, di­ag­nos­tic cal­i­bra­tion will be­come even more rel­e­vant to the DIY re­pairer as these ve­hi­cles be­come older and newer ones be­come more so­phis­ti­cated.

Un­for­tu­nately, while you might be able to read the fault codes, no DIY di­ag­nos­tic equip­ment is avail­able to cal­i­brate these sys­tems. Hella Guttmann So­lu­tions is one com­pany that has de­vel­oped its di­ag­nos­tic sys­tems for after­mar­ket garages, mean­ing that you are not obliged to visit main deal­ers. The equip­ment com­bines tra­di­tional but high-end di­ag­nos­tic equip­ment with cam­era and sen­sor cal­i­bra­tion (CSC) hard­ware, us­ing ve­hi­cle­spe­cific cal­i­bra­tion boards. There­fore, if you are re­plac­ing com­po­nents on a mod­ern ve­hi­cle (ei­ther do­ing the work your­self or through an in­de­pen­dent work­shop), hav­ing the cam­eras cal­i­brated af­ter­wards is the only way that you can com­plete the re­pair safely.

The pro­ce­dure has sim­i­lar­i­ties to a hu­man eye test and is demon­strated be­low. It high­lights not only the lat­est in di­ag­nos­tic in­ter­ro­ga­tion and cal­i­bra­tion, but also the im­por­tance of global scan­ning and how in­ter­ro­gat­ing one sys­tem might in­flu­ence an­other sep­a­rate com­po­nent. While not a DIY task, we would ad­vise strongly that you ask the work­shop to pro­vide a cal­i­bra­tion cer­tifi­cate that you can file with your car’s ser­vice his­tory.

Au­to­mo­tive di­ag­nos­tics is much more com­pli­cated than plug­ging in a fault code reader. De­cent tools will give you ad­di­tional in­for­ma­tion that will al­low you to make a more ac­cu­rate di­ag­no­sis.

Should you sus­pect that a sen­sor is faulty, you can back probe and mea­sure its val­ues with a mul­ti­me­ter. In many cases, you will need the val­ues from which you can com­pare the re­sult. Ad­vanced di­ag­nos­tic hard­ware can pro­vide this in­for­ma­tion.

On newer cars, the spec­i­fi­ca­tion is not al­ways ob­vi­ous un­less a global di­ag­nos­tic scan is per­formed. This dis­tance radar sen­sor fit­ted to a four-year-old VW Pas­sat is hid­den from view be­hind the front badge.

Cer­tain ac­ces­sories that are fit­ted and in­te­grated to Can­bus wiring sys­tems re­quire pro­gram­ming us­ing di­ag­nos­tic tools and the EOBD port.

Live data is an im­por­tant as­pect of di­ag­nos­tics. In some cases, such as this live throt­tle po­si­tion data, the info it­self might be ir­rel­e­vant. In­stead, you are look­ing for pat­terns, such as the throt­tle pedal move­ment be­ing rep­re­sented ac­cu­rately on the graph. For mea­sur­ing sen­sors out­side of the EOBD socket, an os­cil­lo­scope is an in­valu­able tool.

Some generic tools might al­low you to ac­cess spe­cific ECU func­tions for main­te­nance work. For ex­am­ple, this one in­cludes con­trol­ling the elec­tric park brake ECU, which is es­sen­tial for the safe re­place­ment of fric­tion pads.

Good-qual­ity di­ag­nos­tics will also di­rect you to the lo­ca­tion of the EOBD socket on your spe­cific car.

Wa­ter ingress into this socket might cause the ECU to as­sume that the com­po­nent is faulty, while the real is­sue lies with the wiring.

More ad­vanced di­ag­nos­tics will pro­vide in­for­ma­tion on wiring di­a­grams, com­po­nent spec­i­fi­ca­tions and even part num­bers.

Con­sider in­vest­ing in other di­ag­nos­tic tools, such as a pres­sure gauge (as shown), which gives an ana­logue read­ing of par­tic­u­late fil­ter pres­sures that can be com­pared against the data pro­vided by the di­ag­nos­tic equip­ment, as it may be cor­rupted by a faulty pres­sure sen­sor.

◀ Os­cil­lo­scopes are use­ful di­ag­nos­tic tools, es­pe­cially if you have a PRE-EOBD car. They test the in­put/ out­put sig­nals of a com­po­nent, but you need to in­ter­pret the on-screen dis­play. Os­cil­lo­scopes are not cheap, but they are a good in­vest­ment if you know how to use them.

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