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VW Jetta EPC light keeps coming on and car goes into limp mode.

Why does EPC light on...

Why does EPC light on VW Jetta keep coming on and then the car will go into limp mood? What does that mean?

If I shut down the car and reset it, the light turns off but will come back on about every 100 miles. I just put a brand new battery and spark plugs in. Please tell me what this light means. I do not have a owners manual.

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Answered in 1 hour by:
6/1/2008
RAFALEE
RAFALEE, VW Technician
Category: VW
Satisfied Customers: 5
Experience: VW MASTER TECH. ASE MASTER TECH. SPECIALIZING IN EMMISION & ENGINE MANAGEMENT, BODY, CHASIS, SUSPEN.
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EPC stands for Electronic Power Control. this means that your vehicle has a fly-by wire system, which means that there's No accelerator cable and the throttle body is controlled by the ECM (Engine Control Module). The Accelerator pedal (or gas pedal) it's just a sensor, so no mater what your input is on the pedal the ECM actuates the throttle however it wants. But have no fear, the Accelerator Pedal Module hoses two TPS sensors(Throttle Position Sensors), G79 & G185, this two produce an increasing voltage as you press on the gas pedal, but at different rates for safety, the Throttle Body Control Module J338 (throttle body) also has two sensor G-187 and G-188, as well as Throttle Drive Motor G186, G-187 and G-188 the output voltages mirror each other for safety reasons.

Back to your EPC light, when you say reset it, do you actually clear the fault codes with a scanner, or you just cycle the ignition switch? Either way if a fault for the brake light switch is present, this means most likely your problem is the brake light switch, some cases that brake light switch does not trigger a fault for still malfunctions and triggers an EPC related code, I would replace the brake light switch, clear faults and test drive the car.

So if you have anymore questions or if you can provide me with more info on the fault code numbers and descriptions, and if your vehicle is manual or automatic, please do.

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Customer reply replied 9 years ago

Manual, cycle ignition switch to clear fault. I have taken in to mechanic shop but cant find codes.

Ok, if your EPC light comes on there will be a fault code stored in the ECM, any generic scan tool will give a P-Code (a fault code with a P on the beginning), cycling the key does not clear faults, it only resets itself until the fault returns. Is this a manual or automatic?

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Customer reply replied 9 years ago

Does brake light switch over ride throttle sensors? It is a manual.

No it does not, what happens is that the ECM sees an incorrect signal from the brake light switch. For example it sees your pressing on the gas an at the same time your pressing on the brake and it will get confused.

Or if you have a fault with a pedal sensor or a throttle sensor, have you had your brake light switch replaced?

RAFALEE
RAFALEE, VW Technician
Category: VW
Satisfied Customers: 5
Experience: VW MASTER TECH. ASE MASTER TECH. SPECIALIZING IN EMMISION & ENGINE MANAGEMENT, BODY, CHASIS, SUSPEN.
Verified
RAFALEE and 87 other VW Specialists are ready to help you
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Customer reply replied 9 years ago

No, I haven't replaced the brake light switch.

I would replace the brake light switch first, it's the easiest and relatively inexpensive. If you could come up with fault codes it would be much helpful. I don't understand why the repair shop say there were no faults.

Usually when an EPC light triggers it stores a fault in the ECM, since it's part of the ECM, they added another light (the EPC light) because the Check Engine Light is more emission related issues only. So in order to alert you of an Electronic Power Control fault they added a light.

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Customer reply replied 9 years ago

I'll try that because your the only one that could tell me what EPC was I wish I could find a program for laptop like at work to read my car.

Try Ross-Tech.com to get more information.

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RAFALEE
RAFALEE
RAFALEE, VW Technician
Category: VW
Satisfied Customers: 5
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Experience: VW MASTER TECH. ASE MASTER TECH. SPECIALIZING IN EMMISION & ENGINE MANAGEMENT, BODY, CHASIS, SUSPEN.

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