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If you're thinking about buying a mk4 (mark 4, mkiv, 4th generation) Volkswagen TDI or just bought a new car (at least new to you), here's a maintenance checklist to bring your car up to good running order, list of common problems, FAQ, and other things to know when buying. A full list of "how to" is linked above. A general TDI FAQ, more buying checklists, and technical index can be found at 1000q: FAQ and "how to", the blue button on the upper right. Register for the forums linked at the top to ask any questions about this article.
Why would you want an older TDI instead of a brand new TDI? The 1998-2003 TDI get the best fuel economy amongst TDI sold in North America because the cars were lighter, the engine very efficient, and have lighter emissions standards than new cars. Later TDI sacrificed fuel efficiency to meet emissions and grew in size/weight/features/power (which could also be the reason why you want a newer TDI).
This body style/generation had two engine types, "pumpe duse" and regular direct injection. For North America, 1998-2003 mk4 VW TDI are regular direct injection using a Bosch VE distributor fuel injection pump. 2004-2006 are pumpe duse injection. See 1000q: mk4 Jetta cosmetic differences and 1000q: direct injection vs. pumpe duse vs. common rail for more details. 2004-2005 VW Passat TDI are also pumpe duse but since they use a different engine and body, see 1000q: Passat TDI new owner checklist for information on those.
There were two basic trim levels. GL = basic trim. Generally speaking, GLS = power windows, sunroof, alloy wheels. There were some trim changes over the years so early cars typically don't have stability control or traction control. While you can retrofit traction control (brakes the wheels at low speeds to help get you moving), it's nearly impossible to add stability control (yaw control at higher speeds to straighten out a slide). Some other options were leather, monsoon radio w/6cd changer, automatic transmission, and sunroof.
1999: Beetle adds side turn signal behind front fender. ABS standard on new beetle
2000: Immobilizer anti-theft device in key standard, some models receive clear side marker lights, trunk entrapment inside release latch added, brake wear indicator light on dashboard
mid 2001: side airbags standard in Jetta, head curtain airbags optional in Jetta, standard in Golf, trunk entrapment latch standard
2002: Jetta available as TDI wagon, new 2 din stereo system with optional cd changer option, monsoon stereo is also changed, cd player standard on GLS, Golf GL now available in 4 door
2002-2003: ESP stability control becomes an option on all models
2003: New wheel styles introduced, base GL now includes power windows/locks, cd player, and cruise control standard (all base cars), GLS now includes alloy wheels and moonroof standard.
2004: Pumpe duse engine introduced (click here to see the differences between direct injection and pumpe duse), Passat now available with diesel engine in the US, Passat wagon now available as TDI (auto transmission only), side head curtain airbags standard, Auto transmission now 5 speed instead of 4 speed (the 5 speed is much more reliable), Jetta is slightly restyled (click here to see the differences), Monsoon premium stereo standard on GLS
2006: ESP stability control standard on US Volkswagens
Check your local laws for any tax benefit or exemptions for high mileage cars. All known tax credits and exemptions are listed at 1000q: TDI tax credit and exemptions.
Do the car have constant low power, is rev limited, or suddenly loses power? See 1000q: constant low power and 1000q: sudden limp mode diagnosis.
Autozone or your local auto parts store give free error code scans. See if there are any error codes in the car computer's memory. Not all errors will set off the check engine light (CEL) or malfunction indicator light (MIL). This will give you a hint of any major problems. If you plan on working on the car yourself, get the VW/Audi specific VCDS ross tech car diagnostic cable. It used to be called vag-com. Caution: early VCDS software causes a conflict with the airbag module in 2000-2001 mk4 and possibly other years as well. If you have a VAG-COM, upgrade it to the latest version. Refer to the ross tech website for the final word on the airbag problem, more details at http://www.ross-tech.com/vag-com/vw_issues.html . If you autoscan or try to scan the airbag module with earlier software, it could cause the airbag module to show an error and light the check airbag warning light on the dashboard permanently! When using a cable, make sure the green LED on the cable shows up to confirm hardware compatibility if equipped with an aftermarket radio.
Some common codes are related to worn vacuum lines or the glow plugs. If the glow plug harness has a bad connection this will set off the CEL. Check for corrosion on the wires or breaks. Note: glow plug number is opposite the cylinder number because it goes in closest to the harness. Cylinder 1 has glow plug #4, cylinder 2 has glow plug #3, etc. Only 2002 and newer differentiated glow plugs, older cars only recognized all or none.
Varies according to the year/engine so check your owner's manual for the change interval. Early cars with the lower 60,000 miles or less timing belt parts can have the 100,000 mile timing belt retrofitted. (You must also change the tensioner, rollers, and water pump.) If this part fails, the cylinder head will be damaged and in severe cases you will need a new engine. All interference engines which use a timing belt will have engine damage if the timing belt or timing belt roller/tensioner fails because the valves will hit the pistons. For 1998-2003 TDI ALH engines, see 1000q: timing belt part 1 for a detailed procedure. The automatic transmission cars have lower timing belt change intervals for some years because the larger injection pump puts more stress on the timing belt. For 2004-2006 BEW pumpe duse engines, see 1000q: pumpe duse timing belt part 1.
If you just purchased this car, many sellers will have the timing belt changed to add value to the car. Many don't know how to properly index the tolerances that a diesel engine needs or the procedures for replacing the timing belt on a TDI. Some have used a mechanic who is familiar with gasoline cars and messes up the TDI engine. At least remove the timing belt cover and inspect the parts to see if they look new as some sellers will outright lie. If you have any doubt about the timing belt, have it changed as soon as possible not as soon as practical!
10,000 mile change w/filter if you are using synthetic engine oil for diesels. See 1000q: diesel engine oil for a list of direct injection (non pumpe duse) engine oils. See 1000q: pumpe duse engine oil for a list of oils approved by VW for pumpe duse engines. Generally speaking, long oil change intervals are good for the engine assuming that you use the correct engine oil. It's normal for the oil to be black, even when new. See the engine oil lists for more details. See 1000q: oil change procedure for the DIY procedure.
While you are under the hood, see if the splash shield is there - it's a black plastic shield that covers the bottom of the engine bay. If you can see the ground through the engine bay, someone lost it. It should be replaced to keep water and dirt off the bottom of the engine and belts. If you see a metal shield, someone upgraded the plastic shield to protect the aluminum oil pan.
Tire air pressure: as specified by the manufacturer. There is a sticker inside the fuel door, on the inside of the driver's side door, or in the trunk which will specify an appropriate cold tire air pressure. Check tire pressure when the tire is cool or you haven't driven the car in at least 5 hours. A generic tire pressure for an average weight passenger car is 32 psi. Never exceed the cold tire pressure listed on the side of the tire.
Engine coolant: lifetime coolant should be changed as necessary. VW/Audi G12 (G12+) or Pentosin coolant is red, pink, or purple. Do NOT mix G12 with other colors (green, blue, orange) otherwise it will sludge the coolant. If it has to be topped off, use distilled water. If you are topping it off more than once, first figure out where the coolant is disappearing. See 1000q: coolant flush or change for more details and pictures.
10,000 mile drain water, 20,000 mile replacement. If you plan on using high percentages of biodiesel, you should change it as soon as practical because biodiesel can loosen up deposits. See 1000q: fuel filter change for more details. See 1000q: intro to biodiesel for more info on biodiesel.
This is a rare but bizarre condition where coolant will seep into the wiring harness due to a faulty coolant tank, traveling throughout the wiring harness and damaging electrical components. This can total your car because in extreme cases, coolant can seep all the way back to the taillights and corrode all the electrical contacts! See 1000q: coolant migration for more details. It only takes 5 seconds to check and is a rare condition.
98-03 cars had a relay marked 109 which commonly overheats and fails, shutting the engine off suddenly without any notice. Relay 109 powers the ECU (car's computer), so no ECU = no fuel and sudden engine shut off. The old relay is black, marked "109" (601 if you're upside down), and is under the dashboard in the relay box. The redesigned relay marked "109" is gray and fixes the problem. If you have a black relay 109, get it replaced ASAP with a gray relay 109. An indicator of a bad relay 109 is the engine suddenly shutting off and the glow plug not coming on during failed restarts. Sometimes the relay will cool down, letting you start the car after a few minutes.
Diesel injection pump leaks (1998-2003 only) - Due to age and fuel issues, the seals on the injection pump can leak. Leaking diesel fuel can corrode the timing belt and coolant hoses so even a small leak should be cleaned up asap. The top cover, middle quantity adjuster section, and head o-ring can be replaced on the car but most of the other seals should ideally be done off the car. The pump should not be removed without locking the timing belt with VW timing belt tools since it's on the timing belt drive. See 1000q: injection pump top cover replacement for more details on top seal replacement. Warning: only the top cover seal can be easily replaced, the other seals require a VCDS and at least basic mechanical sense and the proper tools.
Tandem pump leaks (2004-2006 only) - The tandem pump is a dual fuel and vacuum pump on the driver's side of the engine head. It carries fuel to the pumpe duse injectors and is found on 2004-2005 mk4 cars (also used on mk5 cars) The earlier cars' fuel pump was for vacuum only. There was a recall on the tandem pump seal leaking. If diesel fuel leaks onto the rubber parts, it will corrode the rubber hoses.
Should be changed every 2 years regardless of mileage with DOT 4 fluid. See 1000q: brake / clutch fluid flush for some tips.
(all diesel engines) If the engine ever suddenly races and accelerates on its own, it may be having a runaway. All diesels could experience an engine malfunction which causes the engine to eat its own engine oil. Since diesels are throttled by fuel and not air, this causes a feedback cycle in which the engine races higher and higher. If the car is in gear it will also accelerate. The first priority is to keep control of the car and shut off the ignition as soon as it's safe and practical. Take it to a mechanic before starting it again. Read more about a diesel engine runaway and some causes at 1000q: Runaway diesel engine FAQ. All ALH engines have an anti-shudder valve which cuts off air to the engine. Some people remove it and put in aftermarket "race pipes" to increase power. I don't use them because it removes the emergency engine shut off feature.
(2004-2006 mk4 TDI only) - VW switched to ceramic glow plugs starting with the 2004 TDI. In 2009 they issued a recall which replaced the ceramic glow plugs with steel but didn't do sufficient testing on the computer flash for the new glow plugs. This can result in significant cold start problems if the car is started in near freezing temperatures or even a no start condition. If you had the recall done VW will fix their mistake with an update, if not they won't. See 1000q: glow plug recall related cold start problem FAQ for more details.
If you are thinking of buying a 2004-2006 TDI, do a camshaft inspection. See 1000q: Pumpe duse engine camshaft lobe inspection/replacement for a detailed procedure. This is not something that most mechanics would inspect so it isn't included in the immediate checks. But before doing the next timing belt service (2004-2006 cars only), remove the valve cover and inspect the camshaft. The camshaft on 2004-2006 ( pumpe duse engines) have narrow camshaft lobes because some space is taken up by the extra injector lobes. VW also specified too thin engine oil. Some engines have experienced excess wear on the camshaft lobes or the lifters whih will cause running problems and in extreme cases, cause the timing belt to seize and skip. Look for flattening of the lobes or cratering of the lifters. Again, this is for the pumpe duse engine only found in the 2004-2006 engines.
On 1998-2003 cars, check the fuel injection quantity through VCDS. Some cars tend to have running problems or smoke due to poorly calibrated fuel injection quantity. See 1000q: injection quantity adjustment and testing for more details. This can also fix a shudder when revs drop (like when shifting into neutral).
The diesel fuel injection pump on 1998-2003 cars have had a few bad fuel temperature sensors. If you go to the dealership, they will try to sell you a new injection pump. It is user replaceable, see 1000q: fuel temperature sensor replacement for a detailed fix. Pumpe duse cars also have a fuel temp sensor but it's on the fuel feed line near the tandem pump on the head.
The center console HVAC light often burns out. Just pull out the center knob straight out to reveal the light bulb. The knob and the bulb are shown to the right.
Due to age and possibly the switch to ultra low sulfur fuel, some people experience leaking seals on the fuel injection pump (only for 1998-2003 models). This will cause a no or hard start condition due to the fuel pump losing it's prime. The dealership will not fix it, their only option is to replace the entire pump at great expense. It's easy to change a few of the seals on the car as long as you have the right tools and basic mechanical skill.
Always apply the parking brake when parking! It's good practice with any car but it's important on VW because this sets the rear caliper self adjusters. It's best to apply the brake before going into park (auto trans) or first/reverse gear (manual trans) to put stress on the brake instead of the transmission internals. While you're there, jack up a rear wheel and spin it. You may notice the brake pads touching the rotors and a little scraping but any more contact means misadjusted or dragging parking brake. Rusted parking brake cables can also freeze the rear calipers in cold moist weather. See 1000q: parking brake cable replacement for the fix. If the rear brakes smell like hot and burning brakes it is probably the rear caliper sticking or a damaged wheel bearing.
The sunroof water drains can get clogged and leak water into the car. Open the sunroof and pour water into the water drains at the corners. It should easily flow out of the drains at the door hinges. See 1000q: sunroof drain for more details. VW later issued a recall for this issue.
You may want to exchange the plastic splash shield (the black plastic cover under the engine) for a metal skidplate. The oil pan is aluminum and it will crack if it gets hit from a speedbump, pothole bottoming out the car, or a tow truck driver's yoke hitting it. If you hit a bump and notice the engine oil light turn on, STOP as soon as practical and check for oil leaks and the oil level. There is a stronger steel bottomed oil pan available from VW. See 1000q: skidplate installation for more details.
A contributing factor to damaged oil pans is a worn suspension. Replacement of the struts, strut mounts, and front anti-roll/sway bar bushings is recommended if your car has over 100,000 miles or as needed. If your struts are worn out, the oil pan is more likely to bottom out on hard bounces and get damaged. Also, people generally don't notice the mechanical condition of a used car but they do notice how it rides. A good ride can make an old car feel new. Lastly, refreshing a few components makes a big difference in restoring lost handling and adds safety in the event of an emergency maneuver. See 1000q: strut install for more details.
The in tank low pressure electric fuel pump (lift pump, only for 2004+ TDI) can fail and cause low power or engine stalling depending on the model of lift pump. It's not a common problem but if it does happen you know.
The EGR (exhaust gas recirculation cooler) tended to leak on 2004-2006 models.
If doors don't seem to recognize when they are opened, the door module microswitch is broken or there's broken soldering point in the module circuit board. The module cannot be accessed without removing the inside of the door, window, and window regulator. Common symptoms include the door/alarm going off even after you open the door or the interior "door open" light not coming on for 1 door. See 1000q: door module replacement for more details. It's also possible the wiring harness in the rubber boot at the door hinge has cracked.
If the glow plug light is flashing, it could be a bad brake switch (under the brake pedal). There were multiple recalls on the brake light switch under the brake pedal so call VW service with your VIN number or check VW's website to see if it's up to date. If you have an auto transmission, a bad switch will not let you shift out of "park" since you have to brake to release the shifter out of park.
Don't leave the power mirror selector in the middle position if you have heated mirrors and a mk4 (1998-2005 and NB/Golf 2006) VW, leave the mirror selector in left or right. The center position in most cars is "off", but on your VW it's "heat". Leaving it in "heat" when the car is on will burn out the heated mirror element. There is no timer to turn it off, it'll just always be on until it burns out. VW has finally fixed this design quirk in the newer cars by linking it to the rear defroster or a temperature sensor. See 1000q: power mirror glass replacement if you want to remove the mirror glass and heater element.
Replace the vacuum hoses because the ends get dried out, rub through, or crack. They are mostly 3.5mm and 4mm hoses, you can buy silicone hose at Mcmaster. These can cause limp mode, as if you are trying to use more power but the engine suddenly loses power, see 1000q: limp mode troubleshooting for more details.
The MAF (Mass air flow sensor) commonly fails. Symptoms include a gradual reduction in power, stumbling, poor engine running. The solution is MAF replacement. This commonly occurs around 40-100,000 miles. It is covered by an extended warranty for 7 years or 70,000 miles for pre-2002 cars. See 1000q: MAF FAQ and 1000q: MAF replacement for mk4 and mk5 TDI. I do not suggest the use of aftermarket "oiled gauze" high flow air filters because the stock TDI filter as plenty of excess capacity and the oiled gauze oil and dirt could damage the MAF sensor. Also see 1000q: low power.
Do you have an automatic transmission and 1998-2003 model? It uses the "01M" automatic transmission. Expect lower fuel mileage. It has also proven to be less reliable than the manual transmission. Regular fluid changes should help but many feel that the problem is the design of the transmission. The 01M shares many internal parts with the pre-1998 096 automatic transmission. See 1000q: auto fluid change. The 2004 and up auto transmissions seem to be much better and fairly reliable. The good news is that problems seem to creep up rather than suddenly fail. If you are experiencing a delayed reverse or delayed forward engagement, you may be experiencing the onset of automatic transmission failure, seek mechanical advice.
The turn signal/hazard switch had a recall. The hazard switch is also the turn signal relay, it should have been replaced under recall or you can just pull the switch out and replace yourself. A problem that comes up is a clicking turn signal due to dust buildup contaminating the switch. See 1000q: clicking turn signal fix for the repair.
The nut holding on the air conditioning compressor clutch pulley sometimes comes loose, if you are already down there, take a second to check it and tighten it to torque. See pics and torque specs here: 1000q: AC nut fix
If you have a New Beetle, the driver's side door handle often cracks or will crack. The Beetlebrace is a metal brace that will fix or prevent it from cracking. See 1000q: new beetle door handle repair for the fix.
If your car has extreme high miles, some suggest changing the camshaft and lifters around 300,000 miles. Before 400,000 miles, it's suggested to change the oil pump chain and tensioner (under the front cover). It might last to 500,000 but the car has already gone more than twice a normal lifespan so changing the oil pump chain and tensioner is reasonable preventative maintenance. See 1000q: crankshaft front seal for some tips.
As mentioned earlier, the suspension is probably worn out due to age and mileage. While you could go with an OEM suspension, there are many options for sport level suspensions from aftermarket companies. See the strut install article for more details. Chip tuning is very well developed for these engines. The average chip tune can increase power noticeably anywhere from 20-30 hp and 30-70 lb-ft of torque! The difference is if you combine it with larger fuel nozzles and use a clutch that can hold the extra power. If you increase power too much the clutch can't hold the torque.The amount of power varies according to engine health, tune parameters, and supporting modifications. I recommend Malone tuning and KermaTDI because they actively develop and support their TDI tunes.
There were a few early 1998 New Beetle that had the AGR engine instead of ALH engine that all other 98-2003 TDI had. It's basically an ALH engine with a wastegate turbo (older style, no internal vane adjusters) instead of VNT turbo.
If you have locking wheel lug bolts (star pattern instead of 6 sided hex head bolts), the key is in the small pouch in the tool kit. VW switched locking lug styles so if you're missing the key count the points on the bolt and buy one ASAP or have the dealer put in a regular 6 sided hex lug bolt. VW no longer sells replacement lug keys although you can buy aftermarket ones that will fit online. Also check the spare tire wheel well and glovebox because sometimes the lug key is misplaced.
You may also notice that the headlight plastic is oxidized and yellowed. Polishing the headlights will increase the headlight effectiveness and make it look better to. See 1000q: headlight polishing for more details.
If you want to add an iPod adapter, VW sells an OEM kit that emulates the CD changer and will work with the stock radio. See more in 1000q: VW ipod, aux in, and mp3 cable adapter compatibility.
Is there wax like tar dripping from the bottom of the doors? It's......
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