VW: Das not scary auto

I’ve worked in several aftermarket shops over the years and in most of them, the idea of doing anything more than basic servicing on a Volkswagen product (or any other European make for that matter) sent techs scurrying for the nearest exit. But if you’re comfortable tackling more serious challenges on domestic and Asian makes, adding VW to your repertoire need not be as scary as you may think. Here are a few tips on how to make the transition a little easier, and some of the common repairs I’ve seen.

Drivability Diagnosis
Your customer owns a 2004 VW Passat, and you’ve taken care of its routine maintenance for a while. The owner likes your shop, and has come back because she trusts you. This time, the Malfunction Indicator Lamp (MIL) is on and she wants you to fix it.

Your diagnostic process is no different on her Passat as it would be on your GM. First step is to verify the complaint and gather a little information. Your present scan tool likely has a Euro update available, if you don’t have it already, and many aftermarket scanners can supply the data you need to diagnose the majority of problems you’ll encounter. If you have a significant VW/Audi customer base, or prefer a tool with a little more focus, you might consider the Ross-Tech VCDS. The VCDS is a PC-based scan tool that has the look of the older factory VAG tool, with many of the same capabilities. It is very user friendly, easy to get acclimated to, and offered at a very reasonable price. Using the VCDS makes life a lot easier, as you’ll soon learn when you start reading the diagnostic flowcharts in your service information.

Of course, you could try to rely on Global OBDII alone. But that would limit you to engine drivability, and even then you’re only getting half the story. Connect in enhanced mode, no matter the manufacturer, and you’ll get a more complete picture of what is really going on.

One word of caution before you connect any scan tool to a VW. Look to see if an aftermarket radio has been installed. Since 1997 or so, VW radios have had diagnostic capability, reporting to your scan tool on the K-line bus. The connector that joins the radio to the K-line is the same as the one on older VWs without diag capability, but that pin used to carry B+, or 12 volts, on it. If you’ve installed aftermarket radios, you know that they make harnesses that adapt the new radio to the OEM wiring, and in that lays the problem.

The aftermarket harness duplicates the older style radio, and when used on a later model harness, sends 12 volts right to the DLC (Diagnostic Link Connector). Plug your scan tool into that, and most likely it will fry your tool. So before you connect, measure the voltage between DLC pins 4 and 7 with your DMM (Digital Multimeter) with the radio and ignition turned on. If it’s over 9 volts, suspect there’s a problem and don’t connect your tool until it’s been repaired.

VW PIDs
Once connected, you’ll find that VW coding, like other Euro makes, doesn’t follow the Pxxxx format you’re used to. Instead, factory defined numeric codes are the norm. Many of these codes have an SAE equivalent, and many don’t. Access to good service information is one key in understanding code definitions and setting conditions.

OBDII readiness monitor status is referred to as the readiness code, and is a series of digits comprised of 0s and 1s. A 0 means the monitor associated to that digit is complete, and a 1 means it has not completed. Often, the last step in the flow chart is a direction to regenerate the readiness code. If your scan tool has the capability, you can force many of the monitors to run to completion in the bay, and verify your repairs before returning the vehicle to the customer.

Parameter Identifiers (PIDs) are a little different, too. You won’t see a screen with a series of PIDs like you see on domestic and Asian makes. In fact, as far as I know, VW is the only manufacturer that uses this unique format. Every module on the car has a two-digit address — 01 for the engine control module, for example. And each module has PID groups, numbered 001 up to 255. These groups, in turn, have four specific data PIDs VW calls measuring blocks or data zones. In order to access the data you want, you’ll have to have the appropriate group number to see it. Not to worry, the flow charts typically list the groups you’ll need along with how to interpret the information. Group content information is usually available as well, in case you want to look up specific PIDs when troubleshooting a complaint that has no associated code. This format applies to all of the modules on the car, regardless of function, and makes following the VW diagnostic process much easier.

I’ll admit I’m still learning the nuances of VW scan data, and there is a lot more to it than I can share in these few pages. Understanding addresses, groups and measuring blocks, though, is one step in taking the mystery out of VW repair.

A Few Tips
VW has been using electronic throttle bodies since 1996. If power is lost to the throttle body or ECM (engine control module) or if the throttle body has been cleaned, you might end up with a car that won’t do anything but idle or idles poorly. The fix is to perform a throttle body relearn, or alignment. This requires a scan tool capable of performing the procedure and is one good reason for having that capability in your shop, even if all you’re doing is routine maintenance.

MAF (Mass Airflow) sensors are a common failure item, especially when an over oiled accessory air filter has been installed. Weak MAF sensors may or may not have a code to go along with their symptoms. Specs are listed for how much airflow the sensor should be reporting at idle, but even that may not tell the whole story. Better yet, take the car out on a safe stretch of road and perform a Wide Open Throttle (WOT) acceleration from a rolling start, backing off as soon as the upshift to second is made. At the same time, record the MAF reading found in Group 002, Measuring Block 4 or Group 003, Measuring Block 2. Look for airflow to equal about 80 percent of the engine’s rated horsepower at sea level. If the reading is significantly less, a bad MAF is a good call.

Another common failure is the Engine Coolant Temperature (ECT) sensor. Its rubber seal can leak, the sensor itself can become contaminated by cooling system deposits, and the electrical connection between the harness connector and the sensor can fail. Inaccurate sensor readings will trigger codes for cooling system performance that might have you thinking thermostat, and loss of coolant from a hardened seal can result in overheating complaints.

If you do have to open the cooling system, be sure to follow the proper bleeding procedure to get all the air out. On some models, that means removing the cowling to access the heater hoses and pulling one back just far enough to expose the bleed hole incorporated in the hose.

Coil On Plug (COP) coils seem to fail with regularity, typically from extended use trying to fire off worn plugs. Using Groups 14, 15 and 16 will generally provide you with misfire counters you can use to aid in your diagnosis. Be sure to clear the misfire codes first, though, in order to enable the counters. A simple swap of coils between cylinders is usually enough to confirm a coil fault.

VW radios, like many others, have an antitheft feature. Be sure to know the code if you need to disconnect the battery during your repair. You can sometimes find the code in the owner’s manual or on a sticker in or on the glove box. If not, you’ll need two special keys to remove the radio from the instrument panel to access the radio’s serial number.

VW oil dipsticks and dipstick tubes are plastic. They harden and get brittle with age, and simply checking the oil level can be enough to break them. If the dipstick feels difficult to remove, try twisting it slightly from left to right as you lightly pull upwards. If it still breaks, carefully remove the pieces and install a replacement.

And when you’re done with that service, you’ll need to reset the Service Interval message display. Some VW models can be reset only with a capable scan tool. However, if you’re a member of iATN and know where to look, there are ways around that.

While there are unique features involved with diagnosing and servicing VWs, they are still just cars. Their engines have to do the same thing everyone else’s does in order to run. If you spend a little time learning the Volkswagen language, you’ll find yourself adding more to your bottom line.