EPC LIGHT - REVISITED

VW POLO EPC LIGHT 

Most VW Polo, Golf, Audi, Passat and  Skoda  vehicles and probably every other VAG cars appears to have problems lately. In one sentence, the most common of these problems seems to be on obd diagnostics the culprit being the  wiring that interconnect all the electronic modules, aka the OBD II / CANbus. Virtually every car diagnostic test done on several different VAG cars produced the same faults. This implies that they are common, since they are recurring on different owners cars.  I can relate to this from my Television engineering days, when several same-make and same-model televisions all appeared to give the same problems. These VAG cars all seemed to have Intermittent / Implausible messages on the Data Bus and its highly unlikely that it could be the electronic modules themselves that are intermittent. Should this be the case, each and every one of these VAG cars then needs to be recalled because it looks like a defective design or assembly line problem.  But that's  wishfully thinking on my part which will obviously be met with and answer like - highly unlikely.

Wiring harnesses and cable assemblies for electrical buses interconnecting several MOSFET fast switching electronic modules each having an edge connector / plug whether it is gold plated or not, has parasitic capacitance. Add this  to the edge connector resistance and crimped wire contacts inside the plugs makes for interesting intermittent connections. The following list are faults /errors  that showed up on diagnostic tests on cars with EPC light problems, which  gives you some idea what I'm referring to. I've  abbreviated "Powertrain Data Bus" to PDB: in order to stop each fault from running onto two lines. Excessive comms errors and internal control module memory error intermittent are common faults caused by wiring harnesses.

SCAN TOOL ERROR CODES

1) 01312 - Powertrain Data Bus:  - Faulty

2) 18034 - PDB: error P1626 Missing Message from TCU  (Transmission Control Unit)
3) 18043 - PDB: error  P1635 Missing Message from A/C Controller
4) 18044 - PDB: error  P1636 Missing Message from Airbag Controller
5) 18058 - PDB: error  P1650 Missing Message from Instrument Cluster
6) 18270 - PDB: error  P1862 Missing Message from Instrument Cluster 

7) 18055 - PDB: error  P1647 Check Coding of ECUs
8) 18056 - PDB: error  P1648 Failure
9) 18045 - PDB: error  P1637 Missing Message from Electric Load Controller
A) 18097 - PDB: error  P1689 Implausible Message from Elect. Load Controller

B) 18104 - PDB: error  P1696 Implausible Message from Steering Column Controller
C) 18107 - PDB: error  P1699 Missing Message from Steering Wheel Electronics

D) 18057 - PDB: error  P1649 Missing Message from ABS Controller
E) 18259 - PDB: error  P1851 Missing Message from ABS Controller
F) 18090 - PDB: error  P1682 Implausible Message from ABS Controller
G) 18261 - PDB: error  P1853 Implausible Message from ABS Controller

Implausible signal means that it is "intermittent", even intermittent at the time the diagnostic tester was interfacing with the ECU's, TCU's, STC's ABS's, A/C etc... "Missing Message" implies absolutely no contact (Open Circuit) with the respective modules at the time of testing. Since VAG cars became inundated with electronic modules, our individual cars each have a few hundred more electrical connections than the previous generation of cars each and everyone of them subject to the tresses and strains of  the bumps on uneven roads and spirited driving. Add engine heat, steam, dampness and other weather conditions to this equation and suddenly these connections become tarnished over time. Tarnished connections are certainly not electrically sound and one way to clean these contacts is with contact spray but graphite or a grey ink rubber would be more effective to clean the tarnish off the gold plated PCB edge connectors. The Bentely VW manual suggest replacement of the whole wiring harness if  any problems arise but it comes at a cost of  $798.00 and that's for a 2007 VW Polo highline. I would hate to know what it would cost for a 2013 Volkswagen Touareg or 2013 Volkswagen Amrok not to mention 2013 Audi A8 or Audi TT .

VAG cars are really nippy and a joy to drive and I'm certain the bulk of VAG car owners enjoy spirited driving but many many VAG car driver probably regret this since they only experienced  EPC light troubles after they did some real spirited driving. I know this is absolutely true for Audi TT drivers who complained that their cars were fin until they gave it a nice workout. It is obvious centrifugal force, torque, tension, flexing, wind resistance and inertia plays their respective roles on the plugs and connectors. The EPC Light problems above, D through G appears to dictate that the ABS Controller is faulty or its edge connector / plug is faulty or the harness is faulty. B through C suggest that the Steering Wheel Controller is faulty or its edge connector / plug is faulty or the harness is faulty is causing the EPC light  to light up. Numbers 5&6 seems to favour the Instrument Cluster as faulty or its edge connector / plug is faulty or the harness is faulty which causes the EPC light to light up. Number 9 and letter A seems to blame the Electric Load Controller for triggering the EPC light. Numbers 1-4 and 7&8 seems to suggest some other electronic module caused the EPC light to light up. All these modules have one thing in common, they are all associated with the Powertrain Data Bus. In essence any module associated with the Powertrain Data Bus can cause the EPC light on VW Polo or other VAG cars to trigger.

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EPC LIGHT

EPC LIGHT

A few months ago the battery in my VW Polo Classic remote key, gave up the ghost.  I used the remote key to lock the car and set the alarm / immobilizer the night before but it refused to open the doors the following morning. So I unlocked the car with the key.  That’s when I realized that my 2007 VW Polo Classic Highline only has one door lock and that I only had access via the driver’s side door.   Neither the left side passenger door nor the rear doors on either side have any locks keyholes. This didn't surprise me because cutting cost has become the new standard in new car design. By not fitting these legacy locks, the car manufacturer saves the cost of three locks, the internal door mechanisms and the labour cost to install them when the car is assembled.  Multiply this amount of savings by the entire vehicle production for the year and you can surely see their total saving.

The Battery inside the electronic key housing.

That brings me to another cost saver implemented in most cars manufactured during 1996 and later. If you heard about OBD II (On-Board Diagnostics II) and CAN-Bus (Controller Area Network-Bus), you will have some notion what I am talking about. With the implementation of CAN-Bus auto electric wiring has been reduced to a bare minimum.  The average older car had between 300 – 400 meters of wiring, used for its head lights, tail lights, windscreen wipers, horn, dashboard electrics, alarm system, central locking, interior lighting etc, etc ...  Much of this wiring are roughly the same thickness (0.5 - 1.5 mm square) to carry the required current to the various devices.  But inside the engine compartment there are numerous thicker wires for the starter, ignition, air conditioner fan motor, alternator, main supply to the fuse box as well as  earth straps to mention but a few.   All these copper wires range between 1.5mm square – 15mm square, some of which are tin plated to minimize corrosion. Not only is this 400 meters of copper wiring expensive, it also weights a good 60-70 kgs.

By embracing the CAN-Bus technology, manufacturers save on the purchase of about 50Kgs of copper wire. Fifty kilograms of copper wire multiplied by the annual car production gives you some idea of the overall saving. Fifty kilograms taken off the weight of a car also gives it a better 'power to weight ratio' hence making it more fuel efficient.  With CAN-Bus technology,  all the  control modules in the car are interconnected, on a serial data network, each module taking charge of a sub circuit of  the electrical system. These modules are network similar to USB (Universal Serial Bus) used in computer networking.

VW EPC LIGHT

However,  CAN-Bus and OBD II was not implemented to save copper, nor to lessen the weight of cars neither to make cars  more fuel efficient.  It was firstly agreed upon by the EPA, then legislated by several Governments whose countries manufacture cars, to install an EMS (Engine Management System) in every new car built after 1996. This management system would monitor the engine and transmission of the car and insure that 'engine emission levels' stayed within a predetermined margin of compliance.  If this level is exceeded due to engine malfunction, the embedded diagnostic system should be able to recognize it and recorded such malfunction and also alert the driver with some form of MIL (Malfunction Indicator Light). Alternatively turn on the EPC light (Electronic Power Control - epc warning light) and stops the  car from revving up or  inhibit the management system and shut the car down.  The frequency of engine misfires or malfunctions are recorded in code format (vw epc code) designed by the Society of Automotive Engineers (SAE) in the ECU's non-volatile memory which is only accessible by the service agents or by someone with a modern day ODB II / CAN-Bus compliant diagnostic scan appliance.

Anyway let me return to the story of the remote control battery. Off I went to the local VW agent to buy a replacement battery.  I drove  a good 40 Km there  and back but still returned without the battery. It was just way too expensive for a small mercury cell. Problem was, I didn't phone to find out how much it cost. At the price that this VW agent charged for the  fob key battery I could manufacture it myself and it would still be cheaper. So I scouted around at a few photographic shops for this particular battery and eventually found a pharmacy that sold them. Hypothetically, if I bought all the pharmacy’s battery stock and sold it to this VW agents at half their asking price I would in fact have made a very comfortable living.

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