EPC LIGHT
Yesterday my VW Polo just wouldn't start, the engine cranked, but sounded as if it didn't crank fast enough in order to start. A good few hundred bucks later for a new battery, she started just fine. I suppose after four years, one should expect a battery to give up the ghost. I thought it was just peculiar that it died without any prior warning, without lazy cranking or dim headlights or a croaky hooter. Anyway, this morning when I started my VW Polo Highline she had some really serious issues. It just wouldn't rev-up. When I looked at the instrument panel, the amber EPC warning light was lit-up yet she idled perfectly normal. The moment I accelerated there was no power, but could only rev to 1200 rpm, it kinda seemed like fuel starvation.
Only when I revved; it seemed like there just wasn't enough fuel available, it sort of smothered. The Amber / yellow EPC light on the dashboard is normally on when I turn on the car's ignition, as can be seen below, but the moment she starts, the EPC warning light goes off, or resets the EPC light on a Polo, which was perfectly normal as far as was concerned.
I experienced this yellow EPC light issue once before, or at least something very similar a few months ago. I was driving through Melkbos Strand with my VW Polo, traveling at about 100kmph. As I passed a high school where some dudes were playing soccer. The very next thing I saw, was their soccer ball coming over the school fence, it hit the road, bounced a few times and rolled directly towards the front of the car. There was no way I was going to swerve to avoid striking the ball because the pavements were like really high and I didn't want to damage my magwheels. There was also an oncoming car approaching from the opposite direction, so I couldn't even cross lanes to avoid it, I just had to go over the ball. By this time, I had already reduced my speed to about 40Kmph. Somehow the ball got jammed between the undercarriage (sump / front suspension) of the Polo and the road. Instead of it rolling, I could hear it chafing along the asphalt. Then the ball suddenly burst with a tremendously loud explosion.
Immediately the EPC light came on, and there was no power. The car just rolled forward until it came to a halt. My foot on the accelerator had no effect. I tried revving the engine but to no avail, it just wouldn't rev. So I switched it off. A few seconds later I started the car and it started just fine but the EPC light stayed on and now, it at least revved to 1200 RPM. I needed to get off the road or at least to the nearest filling station / garage workshop. So I drove very slowly and even when I tried to go faster the car just wasn't going to go faster that 10kpm, even with my foot flat on the accelerator. Eventually... I arrived at the filling station, switched off the engine and popped the bonnet. I saw my air conditioner condenser was hanging skew. The explosion of the ball under the condenser broke the plastic lugs that was screwed to the body. The screws were still in the lugs but the condenser was hanging out below my front bumper. So I went and bought some cable ties at the local supermarket and re-secured the condenser as a temporary measure.
I then restarted the car. The EPC light was still on, so I borrowed a spanner at the filling station and disconnected the battery. Since the Polo was all electronic, I figured it would be equivalent to a computer cold reboot when I reconnected. So, after a few moments I reconnected the battery and started the car. The EPC light was off and I could rev the car as normal. I was so chuffed because I could see myself driving home, all of the 70km distance at 10kpm. When I concluded my business in Melkbos, I was on my way home, about 5km from Melbos Strand when suddenly the EPC light come on again, and once more there was no power. Even with the accelerator pushed-in all the way to the floor, I was still just getting 10kpm. I came to a halt, disconnected the battery for the second time then reconnected it after like 2 minutes, which seemed to have cleared the problem and the engine revved just fine. For the rest of the day the Volkswagen Polo behaved.
The graphic below shows all the dashboard lights amongst which are the Trailer towing mode indicator light, the Electro-hydraulic power steering malfunctions light, the Fog-lights operation light, the Rear seat lock warning light, the Cruise control light, the Unauthorized key electronic immobilizer continuous flashing light.
What I came to discover later, is that there are 2 knock sensors placed at strategic positions in the engine block, 1 per 2 cylinders. So, any engine noise louder than the knock sensor's preset decibel level, will activate them. This in turn triggers the Engine Control Module (ECU) which then cuts the power via ODB II CAN Bus, thus saving the engine from further mechanical damage. However, in my case this wasn't engine trouble but rather an external factor with the same result. The knock sensor or sensors picked up the loud bang of the bursting ball and interpreted it as coming from the engine. That's artificial intelligence for you. What I came to understand much later is that Knock sensor K1 caused the EPC light to come on whereas K2 causes the MIL to come on. If both your EPC and MIL is on it could be K1 and K2 related but this should be determined in conjunction with the DTC which can be read with a scan tool from the non-volatile memory of the ECU. My problem turned out to be the potentiometers on the accelerator pedal that was intermittent. I replaced the accelerator pedal and I've never seen that pesky EPC light again.
FURTHER READING
NB!If you wish to understand how the knock sensor and the EPC light circuits works, read some of my other pages like KNOCK SENSOR, DRIVE-by-WIRE, KNOCK SENSORS EPC EXPLAINED and EPC EXPOSED, EPC REVISITED or EPC DEMYSTIFIED PART 1, PART 2 and PART 3
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