Shining a light on the root cause failure
A headlight fault on a VW Golf shows that getting to the actual problem can be made more difficult if you do not follow the right process
Published: 23 March, 2023
I was recently asked by a trade customer of mine if we could “simply” program a new headlight module for a VW Golf MK7. They had replaced a control unit due to the dipped beam headlamp not operating. They advised me that after the unit was installed the light started working. with the other lights all operating correctly. However, there was a bulb warning in the dash display Please refer to Fig. 1.
At this point the request would seem normal and a straightforward job so we continued with the task in hand. Correctly programming new headlamp control modules on VAG vehicles will require the dealer tool for this manufacturer, known as ODIS (Offboard Diagnostic Information System). I connected this tool to the vehicle and carried out a full system scan. This is a common practice when attempting to program any control modules as programming errors can occur after the process is done and having a report before and after the programming is very beneficial. It can also aid in any warranty claims. As you can see the only fault codes being set are “Headlamps No Basic Setting” and another fault code relating to “Right Headlamp Power Output Stage.” Please refer to Fig. 2. These codes were both permanent and would not clear. I expected to see the basic settings code, as the control module had not yet been programmed. However, the other code seemed odd to me initially.
Why programming is rarely straightforward
I pressed on and attempted to carry out the basic settings of the right-hand headlamp dipped beam control module, which our customer had replaced, but I kept receiving a communication error, as seen in Fig. 3. This seemed very odd as there were no communication fault codes present and all the front lights were operational.
After a few failed attempts I believed there could possibly be another issue with this headlamp which was not analysed initially by the original garage. Using the dealer tool, I accessed the information section and reviewed the wiring diagram for the headlight.
As you can see from Fig.4, there is a main voltage supply, ground, and CAN communication wiring to the headlight. A quick check of each revealed what one should expect when operating properly. Using an oscilloscope, I then checked the CAN bus wiring at this headlight.
To my surprise the CAN bus data signal was corrupted. This seemed very odd. Although the headlight was operational and no-fault codes were present at all regarding CAN communication, it was clear that there was an obvious issue with the data network. There could not have been any communication taking place between the control units on this network. These include the headlight regulation control module and the right/left headlight control modules. After disconnecting each control module in turn, I found the CAN Bus signal had recovered only when disconnecting the right-hand headlamp assembly.
The oversight
It was now obvious that there was more than meets the eye with this job. After contacting the customer and advising them of my findings they agreed for us to carry out further diagnostic work and identify the cause of the shorted CAN bus signal. The CAN bus wiring connects directly into the headlamp, from the connecter, and then into a control unit. According to the diagram, the connector is part of the headlamp assembly. I removed the right-hand headlamp assembly and located the control module which the CAN bus wiring goes to. I removed the headlight control unit from the bottom of the headlight assembly and found water intrusion present, causing the CAN bus signal to be shorted. See Fig.7. Unfortunately for the customer, this vehicle required a new headlight assembly and control module.
A replacement headlight control module and headlamp assembly were both installed. The basic settings function was run once again, using the dealer equipment. This time the function was successful. The headlights needed to be put into a setting position and then physically adjusted on a beam setter before confirming the adjustments were complete. The module then saved this adjustment as its basic setting. What initially seemed a straightforward job turned into a bit of a nightmare due to incomplete diagnosis. Many aftermarket garages will often not allow the diagnosis to take place elsewhere. I carry out a lot of programming for various independent garages across the South West and find this can be a regular occurrence. Correct reporting is essential. Before-and-after reports are a necessity and will often protect you against any shortfalls in the initial diagnosis. These reports include full system scans before and after the programming has taken place, and any other reports generated by the diagnostic tool in use for both failures and successes.
- AS-PL: New alternator
A new alternator suitable for a number of vehicles produced by the VAG group has been released by AS-PL. The alternator is a product of the AS brand and comes under its Standard line. It can be used for the Audi A3, SEAT Alhambra, SEAT Ateca, SEAT Kodiaq, Skoda Octavia, Skoda Superb, VW Arteon, VW Caddy, VW Crafter, VW Golf Altrack, VW Sportsvan, VW Golf VII, VW Passat, VW Passat Alltrack, VW Sharan, VW Tiguan and VW Touran.
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- AS-PL starter
A starter compatible with the Audi A1, Audi A3, Audi Q2, Seat Altea, Seat Leon, Seat Toledo, Skoda Karoq, Skoda Octavia, VW Beetle, VW Caddy, VW Golf Plus, VW Golf Sportsvan, VW Golf VII, VW Jetta, VW Polo and VW Touran has been released by AS-PL. The new starter is the product of the AS brand, and belongs to the Standard line.
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- No code; No problem?
By Darren Darling
The challenge: A 2009 VW Golf 2.0 TDI with recurring DPF problems and no fault codes stored.
This low mileage Golf was presented to us after an unsuccessful trip to the main dealer where the customer was told there was nothing wrong with the car. The customer’s complaint was that the DPF warning light would illuminate every 100 miles; MPG was poor and the car was smoking excessively during regeneration (white smoke). As always, we carried out a thorough assessment of the vehicle to find out why the car was having these issues.
I suspected that the lack of any fault codes was the reason the owner was told that the car was fault-free but clearly we had an issue as the car should not be in regeneration so frequently. We quickly determined this was not caused by a blocked DPF as the DPF was very clean and there were no mechanical issues with the car.
Extended road test
Our next step was to carry out an extended road test while recording live serial data. If the customer had predicted correctly then we would see the DPF symbol illuminate in the next 20 miles or so. Sure enough, the light came on during the road test and the vehicle initiated DPF regeneration. This now gave us an opportunity to monitor the car during regeneration to see what was going on. We noticed that our temperatures during regeneration were too low and that the car did indeed smoke very badly.
Because of the low temperature, the duration of the regeneration was also excessive, taking over 40 minutes to complete. This is not uncommon and we have seen this caused by a software issue on many occasions. We then consulted our database and could see this exact problem with the software version so our next step was to carry out a software update and repeat the extended road test.
The car was noticeably smoother and quieter following the update but it did not initiate regeneration. Although a good sign, we had not seen any evidence yet that it had improved. So, we headed back to the workshop to carry out a forced regeneration so that we could monitor temperature, smoke and regen duration.
We were now happy with the temperatures; the excessive smoke had gone and the regen duration was back to normal. We were confident that the software update had fixed the car.
This job highlights the need for the independent workshop to invest in the correct tooling to carry out software updates because they are becoming more common. No unnecessary DPF cleaning was required to sort this DPF problem out and no parts were fitted to the car.
Another job done and another happy customer.
- Par for the course: VW Golf R mystery, part one
It’s not often you get two bites of the same cherry, but in my case, it happened just one week apart. The story begins many months ago with one of our regular customers. The customer in question is a real enthusiast and a keen track day driver. His car of choice is a Volkswagen Golf R.
Having modified the car over several months, we now have a 500 BHP-plus Golf. It has KW variant 3 suspension with Eibach roll bars, a floating brake disc upgrade, and lightened shell, roll cage etc. It also employs a MBQ electronics platform. I could continue but I think you get the idea.
It’s fully fettled, but even with the best kit and care, you are bound to have something go wrong eventually. Can you guess what happened? That’s right, a problem occurred!
Lack of power delivery
During a track session the car suffered a lack of power delivery, with no abnormal symptoms, misfire, oil consumption noise or vibration.
The Initial investigation began with a serial scan with no DTS present. It is at this point a diagnostic strategy should be put in place. The phrase ‘first look’ involves the principle of gathering as much information without intrusion as possible.
Where to start and which option to take depends very much on the symptoms. In my case the initial tests were conducted in my absence.
A full load data log indicated a specified and request turbo boost pressure of 2.8 bar absolute, with an actual value of 2.3 bar indicated. These values will no doubt illustrate the level of modifications to the power train. The car still delivered a powerful drive experience although the actual power experienced was less than expected.
Well-established test process
This is a common problem and with a well-established test process. The charge pressure circuit was pressure tested without any external leaks. Because the en888 engine does not employ an EGR valve, we did not believe that the cause could be the result of internal leaks. Our first idea actually pointed towards the hybrid turbo, which we initially suspected as the prime cause of the ailment.
I was asked to call into the workshop to review the results so far. I suggested a NVH in cylinder profile be conducted. This engine employs variable camshaft timing on both cams with lift extension on the exhaust cam. With this in mind, I was especially interested to examine the valve piston relationship and the valve pocket profiles.
The results immediately confirmed significant errors to the intake and exhaust valve pockets with excessive exhaust pressure. This engine variant should have little or no pressure above 1 atmosphere, or 1,000mb. during the exhaust stroke, my test results confirmed over 1,700mb absolute. Valve pockets represent the pressure differential across the four-stroke cycle and accurately represent the mechanical efficiency of the Otto Cycle. This is often referred to as pumping losses. So, we have a restriction in the exhaust stream, turbo, catalyst or exhaust system? Removing the flange pre-catalyst enabled examination of the turbo hot side and catalyst intake.
Reduction of boost pressure
The catalyst substrate was detached and turned through 90 degrees. In this way, we discovered the symptoms. A restricted exhaust was reducing both air intake volume, therefore load calculation, and turbine volume. The result was a reduction of boost pressure.
Next, we needed to discover the cause. Excessive heat and expansion, followed by the catalyst detachment. This was interesting, not least because a recent upgrade to the fuel priming system resulted in the fitting of an upgrade in tank pump. The result of which only became known after a track session where a drop-in top-end power resulted in a DTC rail pressure negative deviation.
The pump module, a specific upgrade from a respected independent VAG tuning specialist, had been supplied with the incorrect o ring. This resulted in a slight drop in both flow and pressure together with cavitation causing a lean mixture ratio at extreme load.
So now we have the complete trio, fault, symptoms, and cause.
Happily ever after?
That is not the end of the story however, as this particular VW Golf R returned just a week later. The good news was the owner’s report of exceptional performance. However, the bad news was that with the returned power came horrific vibration.
That’s a story for another day though.
- HELLA new to range additions
Hella headlight units, fog lights and spark plugs featured in the 23 new products introduced late in 2020. The company introduced 17 new headlight units and two fog lights, with the new additions including headlight units for the VW Touareg.
