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Skoda Octavia 1.6 BFQ without LPG - Check engine error and EPC

kubas10 11385 17
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Treść została przetłumaczona polish » english Zobacz oryginalną wersję tematu
  • #1 16654749
    kubas10
    Level 25  
    Hello, I've been fighting with skoda for a long time. Once in a while after starting the engine or while driving, EPC appears and the power drops. Errors:

    17950 throttle positioner potentiometer - abnormal signal;
    17698 coolant temperature sensor at radiator outlet - signal too high;
    17987 throttle control unit - incorrect adaptation;
    17953 throttle control - malfunction;
    17973 throttle control unit - lower limit not reached;
    16486 air mass meter - signal too low;
    17579 throttle positioner potentiometer 2 - abnormal signal;
    17851 sensor for exhaust gas recirculation - signal too low;
    17811 exhaust gas recirculation system - control deviation between setpoint and actual value;

    Within a few months, the following were exchanged:

    EGR, coil + candles and wires, flow meter, throttle + adaptation, ignition block, battery and main relay (original).

    It seems to me that the problem appears in the joint supply of these elements, but I have already run out of ideas. Sometimes it returns the error "main relay malfunction" - even after replacing with a new original.

    What to do with it?
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  • #2 16654763
    sulof1601
    Level 26  
    Hello. It is necessary to check the power supply and ground of the motor controller.
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  • #3 16654783
    kubas10
    Level 25  
    Is there a common throttle, EGR, flowmeter and radiator outlet power supply?
  • #4 16654801
    sulof1601
    Level 26  
    There is no common power supply, EGR has one except the controller from the relay and the flow meter also has power from another relay but the rest of the wires go directly to or from the engine controller. These after the relay have 12V and the others are either 5V or ground or signal.
  • #5 16656736
    kubas10
    Level 25  
    Yesterday I deleted all the errors and rode and it was ok, today after starting the engine the check lit and only one error:

    17851 sensor for exhaust gas recirculation - signal too low;

    Or maybe one of the executive elements causes the above failures? eg EGR come on exchanged ...
  • #6 16656743
    matimon22
    Level 25  
    Have you looked into the ECU plugins and itself? Maybe it's "green" ...
  • #7 16656847
    kubas10
    Level 25  
    I opened the driver and it's ok.
  • #8 16656920
    sulof1601
    Level 26  
    Each controller after opening is ok. Check the basic parameters do not follow the error codes. You also have the function of reading the controller voltage you can check, measuring blocks; flow?, EGR?, Damper? .............. .more data is needed.
  • #9 16656935
    kubas10
    Level 25  
    I would need a motor diagram because I was just out of hgs-data license and I don't have it by the end of the month. How to read driver voltages?
  • #10 16656949
    grala1
    VAG group specialist
    Measuring blocks.
    There will also be a signal from EGR.
    Has the EGR valve been adapted?
    Check installation between EGR and ECU.
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  • #11 16656985
    sulof1601
    Level 26  
    Engine diagram ??????
  • #12 16657108
    kubas10
    Level 25  
    grala1 wrote:
    Has the EGR valve been adapted?


    Yes, after replacing the EGR I did the adaptation, before replacing it during light acceleration the engine tugged.

    Added after 37 [seconds]:

    sulof1601 wrote:
    Engine diagram ??????


    What's so special about it is that you used so many question marks?

    Added after 9 [minutes]:

    grala1 wrote:
    Measuring blocks.
    There will also be a signal from EGR.
    Has the EGR valve been adapted?
    Check installation between EGR and ECU.


    What about the rest of the errors? The throttle also shows that from time to time there is no voltage, on the flow meter ...
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  • #13 16657154
    sulof1601
    Level 26  
    Mmm sorry I pressed it so much ..... and why do you need a motor diagram? Which power supply is lost? Is there no signal or 12V? What about the flow meter? Also the signal is lost?
  • #14 16657251
    kubas10
    Level 25  
    I would like to check under load all the "pros" and "masses" because the fault with me is probably the lack of some power supply at the ECU. The EGR, damper, and flow meter cannot be damaged at once!
  • #15 16657271
    sulof1601
    Level 26  
    Of course not. Enter your driver model and add a pin out and you should find all power and grounding.
  • #16 16657526
    kubas10
    Level 25  
    I don't understand ..., skoda data is octavia I estate, 1.6 BFQ, siemens driver.
  • #17 16657688
    T5
    Admin of Cars group
    Found on the web.
    Attachments:
    • BFQ.pdf (1.21 MB) You must be logged in to download this attachment.
  • #18 16680938
    kubas10
    Level 25  
    The problem was the worn beam under the battery.

Topic summary

✨ The discussion revolves around a Skoda Octavia 1.6 BFQ experiencing intermittent EPC warnings and power loss, accompanied by multiple error codes related to the throttle positioner, coolant temperature sensor, EGR system, and air mass meter. The user has replaced several components, including the EGR valve, ignition coil, flow meter, and throttle, but the issue persists. Responses suggest checking the power supply and ground connections to the engine control unit (ECU), as well as verifying the adaptation of the EGR valve. The user later identifies a worn beam under the battery as the root cause of the problem.

FAQ

TL;DR: One root cause identified, not nine parts: "The problem was the worn beam under the battery." Fixing the under‑battery wiring stopped EPC and power loss. [Elektroda, kubas10, post #16680938]

Why it matters: This FAQ helps Skoda Octavia 1.6 BFQ owners diagnose EPC/check‑engine faults without shotgun part swaps.

Quick Facts

What’s the most likely fix for EPC + power loss on a 1.6 BFQ without LPG?

Inspect and repair the wiring harness under the battery tray. The owner reported EPC and power loss resolved after fixing a worn harness in that location. This fault can mimic multiple sensor or throttle failures. [Elektroda, kubas10, post #16680938]

Which fault codes were actually logged?

Nine codes appeared, including 17950, 17698, 17987, 17953, 17973, 16486, 17579, 17851, and 17811. EPC illuminated and power dropped intermittently at start or while driving. This breadth of codes often points to shared wiring or ground issues, not nine failed parts. [Elektroda, kubas10, post #16654749]

Are the throttle, EGR, and MAF on a common power feed?

No. EGR and MAF receive 12V from relays, while other lines route directly to the ECU as 5V reference, grounds, or signals. Faults across these devices can still share a root cause if a harness or ground is compromised. [Elektroda, sulof1601, post #16654801]

Should I open the ECU to look for damage?

Visual checks mislead. "Each controller after opening is ok." Focus on live data and voltage checks instead of board inspection. Use scan tool measuring blocks to read ECU voltage and sensor status. [Elektroda, sulof1601, post #16656920]

How do I check ECU power and grounds first?

Follow the expert advice: check the motor controller’s power and ground integrity before chasing sensors. Use a load test and verify voltage drop on grounds during faults. Poor ECU feeds can trigger EPC and multiple codes. [Elektroda, sulof1601, post #16654763]

What should I do if only EGR code 17851 comes back after clearing?

Read measuring blocks for EGR command vs. feedback and inspect the wiring between EGR and ECU. A wiring or connector issue can pull the signal low and retrigger 17851. Adaptation can be rechecked after wiring confirmation. [Elektroda, grala1, post #16656949]

Do I need to adapt the EGR after replacement?

Yes. Perform EGR adaptation with VCDS or a comparable tool. The owner adapted the new EGR and reported improved drivability versus prior light‑acceleration “tugging.” Recheck adaptation after any wiring repair. [Elektroda, kubas10, post #16657108]

Can a new main relay still leave a ‘main relay malfunction’ code?

Yes. The owner saw the malfunction return even after installing a new OEM relay. That edge case points to downstream wiring faults, especially in the under‑battery harness. Replace parts only after wiring tests. [Elektroda, kubas10, post #16654749]

How can I read the ECU’s supply voltage in diagnostics?

Use the scan tool’s measuring blocks to read controller voltage and key sensor channels. Compare values during idle and when the fault appears to spot supply drops or reference issues. [Elektroda, sulof1601, post #16656920]

What model and ECU are we dealing with here?

Skoda Octavia I Estate with 1.6 BFQ petrol engine and a Siemens engine controller. This context matters for pinouts, adaptation procedures, and typical harness routes. [Elektroda, kubas10, post #16657526]

My MAF shows intermittent low signal; where should I look?

Confirm its relay‑fed 12V supply, then trace the signal and ground back to the ECU. Because MAF power uses a different relay, a harness fault can still drop signal integrity and log 16486. Inspect the under‑battery run. [Elektroda, sulof1601, post #16654801]

How do I find the right pins to test ‘pros and masses’ under load?

Identify your exact ECU model and obtain its pinout. With the pinout, load‑test each power and ground while wiggling the under‑battery harness to reproduce the dropouts. Record values in measuring blocks. [Elektroda, sulof1601, post #16657271]

Why did so many different codes appear at once?

A single wiring defect can cascade. In this case, a worn under‑battery harness caused low signals and adaptation faults across EGR, throttle, and MAF. One fix cleared many codes, a 1-to-9 ratio. [Elektroda, kubas10, post #16680938]

What quick 3-step process should I follow before buying parts?

  1. Read measuring blocks for ECU voltage, EGR, throttle, and MAF.
  2. Perform EGR adaptation, then recheck live data.
  3. Inspect and load‑test wiring between EGR/throttle/MAF and ECU, focusing under the battery tray. [Elektroda, grala1, post #16656949]

After clearing all faults, only 17851 returned—what does that indicate?

That pattern suggests the EGR feedback circuit remains weak or open. The owner saw only 17851 after a clean slate. Prioritize the EGR signal wiring and connector integrity before assuming a bad valve. [Elektroda, kubas10, post #16656736]
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