Glowing, going, gone!

Top Technician 2017 winner Karl Weaver has joined Aftermarket’s growing roster of expert contributors. Here, he sees the light thanks to a glow plug

Published:  17 February, 2018

I decided to share this case study for my first article because what I expected to be a simple job turned into something a little more complex and gave me an opportunity to study a and learn about a system that until now I’d probably taken for granted.

We were presented with a 2010 Skoda Fabia 1.6 TDi by a car dealer who had recently taken it in part exchange. The engine management was light illuminated, however with no other symptoms. The previous owner told the dealer that the MIL had been on for around a year and her local garage had failed to repair it. It had also recently been recalled for the ‘Dieselgate’ VAG emission software update. The dealer told the customer there were DTCs stored for the glow plugs and that they needed replacing to which she declined as she was sure they had previously been replaced. We already had a reasonable amount of vehicle history to start with, and were ready to take a look.

Voltage and current
A code read revealed DTCs for all four glow plugs being open circuit and a glow plug module communication fault. A quick inspection of the engine revealed that the glow plugs were not that old and also there was a new glow plug module fitted, plus an old one found in the boot.

While checking the resistance of the glow plugs may tell us something, measuring the voltage and current with an amps clamp paints a much clearer picture. The oscilloscope was connected and the ignition was cycled. The screen capture revealed a healthy 12 volts for around 10 seconds then pulsed at random, however there was zero amps flowing (on all glow plugs). It was clear the plugs had gone open circuit for some reason so they were removed for inspection. It was then we noticed that the heater plugs fitted were rated at 4.4 volts, so now we know why they burnt out! Could they be the wrong glow plugs? Could it be the wrong control module? We checked and found the part numbers were correct.

At this point it was crucial that we understood exactly how the system is wired and how it should operate. By studying a wiring diagram we were able to plan how we were going to test the system (see image 1). Starting with the power supplies and ground, it is always best to test a circuit in its normal environment which means we really need the current load of working heater plugs. If we were to fit new heater plugs at this point there was a high risk of them being damaged which is expensive so we substituted four headlamp bulbs instead. The fuse rating for the circuit was 50A so with a quick bit of maths we calculated the current required for four bulbs was safe. The main live feed, ground and ignition switched live were all good so we moved on to the two communication wires that link directly to the PCM.  

If the PCM can log individual codes for each glow plug then we know that it must have a two-way communication system. Scoping both wires with the module connected and disconnected showed us that there was clearly a command signal from the PCM and although it was random and rather messy (see image 2), the glow module responded directly by activating the glow plugs at the same rhythm.

The second wire had totally different digital signal which had to be the feedback to the PCM. The noise and irregularity of the command signal was clearly an issue so we checked the wiring back to the PCM and with the aid of the good old-fashioned wriggle test the fault was identified as a poor connection in the PCM harness connector. The connection was cleaned and the system retested which revealed a much healthier scope pattern and the communication DTC was cleared (see image 3).

Reliable repair
At this point we could have fitted new glow plugs but to save unnecessary expense we wanted to make sure it was a reliable repair so we decided to monitor the system with the faulty glow plugs still installed and the leads connected to the bulbs. We started by monitoring all four glow plug voltages on the oscilloscope. Using the scan tool to activate the glow plugs showed us that the 4.4 volts is achieved by pulse width modulation at a duty cycle of around 13% with a frequency of around three times per second. What was more interesting was that all four plugs were individually triggered in a sequence (see image 4) so there is never more than one glow plug energised at any one time. The logic behind this is that it makes a substantial reduction in power consumption.

Our next test was to observe the control strategy of the PCM from a cold start and warm-up phase. The objective here was to ensure that there was no software related issues. From the point of key on there is a 1.5 second supply phase to heat the plug as fast as possible then temperature is maintained by the 13% duty control.

Decade box
Of course, after a period of time, once the engine starts to warm up the system turns off and the communication wires go quiet. If you want to test it more than once then you’d have to wait for the engine to cool so to save time we connected a decade box in place of the engine coolant temperature sensor and by observing the coolant temperature in serial data on the scan tool we were able to select a variety of resistances that would represent low temperatures and fool the PCM into commanding glow plug activation.

The decade box has proved to be an extremely useful tool really is a must in any diagnostic technician’s tool box. It is great for substituting in place of certain sensors and components to check the integrity of a circuit or to observe an ECU responding to a variation in signal (resistance).

The final test was an observation of voltage over current on one glow plug. The other interesting thing we noticed was the simplicity of the digital feedback signal. By unplugging each glow in turn you could see the pattern in the signal change and when all were connected and working it was a regular pattern.

Summing up
Clearly more time was spent on this job than necessary and the labour charge remained fair. In a busy workshop it is hard to find spare time for these situations but my point is that sometimes sacrificing a lunch hour or staying behind for half an hour gives an opportunity to learn so much which can only aid you in speeding up diagnostic time and process on future jobs.

Winning the Top Technician 2017 competition was unexpected. It has not only introduced me to some very inspiring, like-minded people, but has also taught me you can never have too much training, whether it’s self-training like in this instance or on a professional training course. There are some fantastic training companies offering a variety of courses available now. Also, some of the best and most respected all regularly write for Aftermarket!  





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  • Spin the wheel 

    I have been asked several times about ABS wheel sensors. Like many other components, the technology is changing. The changes reflect the expansion in integrated chassis dynamics.

    Just imagine how many functions require wheel speed and rotational differential data.

    ABS, dynamic stability, hill start, audio volume, navigation, self park, all wheel drive, active steering assist, electronic handbrake etc. Sharing this data on a high speed can network ensures very accurate vehicle motion dynamics.

    Older variable reluctance sensors (VRS) rely on a coil generating an alternating voltage when rotation occurs. The problem is they are not directional sensitive and cannot report motion at very low speed. Air gaps were critical as they affect signal amplitude. They are often referred to as passive sensors. So, the introduction of digital or active sensors was inevitable.


    Principles
    How do we tell them apart? Active sensors require a voltage supply from the ABS PCM, with a ground or signal return. They operate with different principles of signal generation; hall, and magneto resistive. Pure hall effect sensors will switch between the supply potential voltage and ground. Magneto resistive sensors operate on the principle of current and voltage change in response to a change in magnetic induction. This change can be introduced in several ways reflected in wheel bearing and sensor design. Smaller sensors with integrated magnetic field rings are now the norm. Developed by NTN at their Annecy facility they are called encoded bearings. A small ring mounted at one end of the bearing carries a series of north south poles. These have now been replaced by dual encoding, two sets of magnetic rings with a unique offset. This enables the abs module to determine direction of rotation.


    Subtle differences
    There are two very subtle differences in the digital outputs. They can be called pull up or pull down. The sensor supply voltage will be slightly lower than battery voltage this is due to the different internal resistance values. However, it will be around 10.5/11.5v.

    The ground or return signal value will vary between 0v or 1.4/1.8v. You could have a sensor or circuit fault; let me try and explain the subtle differences, and how to prove which is which. Remember the golden rule if in doubt compare a wheel circuit that works normally.

    First unplug the sensor and measure both circuits in the loom. With no load applied the supply voltage should jump up to NBV

    Next check the ground circuit if its true ground then it’s a pull-down type and the signal will be on the power line, and may only be around 200mv

    If a small voltage exists then it’s a pull up type and the signal will be on this wire not the supply. The digital signal will be very small when the wheel rotates. It could be small around 200/400mv, or as high as 0.5/1.8v, depending on the manufacturer variant

    Common sense would dictate the serial route is easiest, however how would you determine an intermittent fault? It could be a faulty sensor, faulty encoder, or a circuit error. The only way is using a scope. Should we measure voltage or current though? Both change in the circuit. Unless you have a very special current clamp, go for voltage and select a AC coupling.

    The specific question I am often asked is current measurement, well I can tell you in a pull-down circuit its around 7-15 ma with a 400mv voltage change. The pull up type will produce around 6/13ma with 0.2/0.35mv.     However, these voltage values can vary due to the value of the two parallel internal sensor resistors these are normally 1.4k ohms, with a much higher resistor in the meg ohm range, within the ABS pcm.

    I hope this helps. The pico image was taken from a VW Golf 1.4 TSI. The easy bit is replacing the wheel sensors. Ever since metal housings were replaced with plastic they never corrode in the housings
    do they…?

  • Four wheel aligner compatibility  

    The Bluetooth Pro Wheel Aligner from Absolute Alignment is fully wireless to ensure fast and easy use, and can be used with four and two-post lifts and in-ground wheel-free scissor lifts. The direct contact charging and calibration system means the whole wheel alignment package is 100% cable free for a safe workshop.  Absolute Alignment supplies an array of wheel alignment equipment to suit workshops of all sizes, and is the only UK provider with a full range of Bluetooth wheel aligners suitable for cars and commercial vehicles – including those equipped with the latest generation of ADAS.

  • 888... Lucky for some 

    With this month’s focus in Aftermarket on cooling, I thought a look at how technology has affected one of the oldest systems of the internal combustion engine. For illustration, I have chosen the Volkswagen Auto Group’s en888 engine, built in Mexico, Hungary and China hence the 888 insignia; It is their lucky number.

    Its one of Audi’s high-performance variants. Its fitted in my Seat Cupra 2ltr, producing 400bhp with stock mechanicals. So, what are the benefits of advanced cooling systems? Heat derived from combustion, transferred by conduction and convection into cooling and the environment is in effect wasted energy. Controlling and where necessary containing it improves efficiency, not forgetting reductions in emission pollution.

    Efforts
    They have made stringent efforts in the mechanical design of the 888 to achieve savings in efficiency. Reducing engine weight, minimising internal friction, increasing power and torque, current with fuel economy initiatives.

    The cylinder block wall is reduced from 3.5mm to 3.00mm. Internal friction is reduced with smaller main bearing journals, revised timing chain design, incorporating a dual pressure lubricating system. The balance shaft has roller bearings, piston cooling jets further improve thermal stability. The jets have PCM mapped control, while extra oil cooling is provided adjacent the filter housing, close to the activation solenoid and twin oil pressure sensors.

    The engine can theoretically reach Lambda 1 from cold within 20-30 seconds.

    Further technical innovations include reduced oil level, reduced tension force in the auxiliary chain mechanism, down shifting achieved with variable valve lift and twin scroll direct mount turbo design.

    Advances
    You will now appreciate that it is no longer possible to separate mechanical design, power delivery, emissions, and all-round efficiency, treating cooling as an afterthought.

    Take the cylinder block design, which possibly has the biggest advances reserved within the cylinder head and coolant control module (water pump). The exhaust manifold is housed completely within the cylinder head casting. This ensures very effective conductance of heat. The emphasis is now on increase, maintain, reduce, thanks to an advanced dual valve PCM controlled coolant control module. The module is mounted at the rear of the engine block, belt-driven with a cooling fan to keep the belt cool.
    By manipulating the two rotary valves, flow and temperature can be effectively controlled within very carefully controlled limits. The rotary valves are manipulated by a PWM 1000hz motor with SENT position feedback (single edge nibble transmission), a method used by the latest air mass meters.

    Heat transfer into and from the turbo is much more efficient due partly to the direct mount and integrated cooling galleries surrounding the exhaust tracts.

    The piston to wall clearance has been increased, with a special coating on the piston thrust side complimenting a direct gudgeon pin to rod contact, the DLC coating removes the need for a bearing bush.

    The cylinder head porting incorporates ignition sequence separation, thus ensuring preceding exhaust pulses do not impede the energy from the current. This in combination with advanced turbine design further improves torque range and downshifting. Cooling control priority is applied to the occupants, then the transmission, further reducing frictional losses.

    Complexity
    Although not directly related to the cooling system, a dual injection system is fitted with its main function being emission reduction. Cold start is provided with three direct injection events, followed by port injection warm up. These systems do not run in tandem. Two thirds of the load range is controlled by port injection, with full load above 4,000 rpm delivered by induction stroke direct fuel delivery.

    From a practical point of view, previous low-tech tasks like replacing coolant components and bleeding now requires electronic support through the serial interface. Using the correct antifreeze is now essential if premature corrosion is to be avoided. As a warning, capillary coolant invasion within wiring looms is well known in some French and GM vehicles, as some of you will be aware.
    It is also worth mentioning that Volkswagen has modified the software controlling cooling in some of their diesel vehicles as part of the emission recall programme.

    Predictably due to their complexity, I can foresee cooling systems being neglected during routine servicing , so expect to see faults as these systems age in the pre-owned market.


  • In the heat of the fault  

    At the workshop we cover all kinds of vehicles, old, new, big and small but with all these vehicles we need up to date diagnostic equipment to be able locate faults within the electrical system.
        
    In the workshop this summer was a 2009 Volkswagen Golf that had an intermittent issue which meant the car would go into limp mode, the cruise control was disabled and the climate control wouldn’t work. Understandably in the weather we were having the lack of air conditioning was a major concern to the customer. No one wants to be without air conditioning in 30Cº.
        
    I plugged in the trusty diagnostics reader and came up with four faults. These included turbo boost sensor, manifold pressure, throttle pedal position sensor and ‘fuel system
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    In my experience cars can throw up all kinds of trouble codes even when there is no issue with that part. I wouldn’t say some manufacturers are more troublesome than others but if a light does appear on the dash it’s best to get it checked out as soon as possible.

    Issues
    I cleared the fault codes and told the customer to see how it drove and if the issues resolved themselves. The customer had the car for just an hour before they called and said that the problem had reoccurred, as much as this is a pain for the customer I always clear the faults and see if it happens again rather than changing unnecessary sensors. I got the Golf back into the workshop and once again plugged the computer in, which brought up one code. This was the throttle position sensor. A quick call to VW and a discussion with their parts people showed that this particular issue can lead to the cruise and climate control not working.
        
    Next day delivery on the part means the car came back in the following day. One bolt, two plastic clips and an electrical connection later and the pedal was off. Gone are the days of the throttle cable. The throttle response is now done by a sensor on the pedal which works out how far the pedal is being pushed and tells the engine how to respond. It is clever stuff,  when it works.
        
    A pedal replacement on the Golf only takes five minutes and another clear of the fault code before taking the car for a road test. On the test drive cruise and climate control were checked as well as making sure no dash lights had appeared.
        
    Modern mechanics have become very computerised. Dash lights appear whether it is indicating an issue with the airbag systems, ABS or engine and diagnostic computers are so important to narrow down what the issue could be. I dislike the reliance that some workshops put on just trusting what appears on the screen of the diagnostics. It is still imperative that mechanics test sensors and look into live data to make sure that unnecessary components are not replaced and the costs put onto the customer, who will have to pay.


  • Exploiting Aircon 

    Although it may be hard to believe given the weather so far this year, but a lot of customers will soon be starting to use their aircon systems only to quickly realise that their system is not working as expected, leaving them hot under the collar! So an ‘exploitable opportunity’ exists as the people in suits might say, but will you be in a position to exploit it most profitably?

    Modern systems
    With the majority of new cars now having some form of HVAC (heating, ventilation and airconditioning system) fitted as standard, it is no longer considered a luxury, just another part of the vehicle’s array of functions that should work when needed – summer or winter.
        
    Many modern systems are designed to be highly efficient and rely on much less refrigerant than previously. Unfortunately, most customers do not understand that the system will naturally leak the refrigerant at a rate of between 10% and 20% per year (depending how often the system is used to circulate oil around the various pipes and seals) and it therefore requires regular servicing and maintenance to ensure continued efficiency. Ultimately, if the refrigerant level gets too low, the system will not operate at all.

    Added value
    The easy way to deal with this is to offer an ‘added value’ service whenever the vehicle is in your workshop – namely a free air-con system efficiency check. If the system does not perform to expectations, or emits a bad odour, then the opportunity exists to sell the service to your customer. So, make sure that you optimise the opportunity that aircon maintenance and servicing presents ensuring that your customers can keep their cool when summer finally arrives.
        
    The fully automatic units available from the leading suppliers will allow full functionality with a minimum of technician’s time – who can still be servicing other aspects of the vehicle while the unit does the work. A printout at the end details what was done and if any problems exist – useful for both the customer and as an activity record for the F-Gas regulations.
        
    If a problem exists with the vehicle air-con system then there is a requirement to diagnose and repair. A good understanding of the principle of operation and system design is necessary to both identify and repair profitably, in terms of time and for fitting the correct parts. The typical mathematics for the return on investment (ROI) are something like (prices as of May 2013 for illustration purposes only):

    Cost of equipment                     £2,795
    Cost of training                         £350
    Marketing materials                   £250

            Total costs:                       £3,345

    Air-con service                          £65 (net workshop revenue)
    2 x air-con services per week     £130 net income

    ROI    3345 ÷ 130 = 26 weeks.


    This excludes any additional repair/parts revenue and is based on only two vehicles per week. With this in mind I really think the decision to invest in the training and technology is a no-brainer.

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