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
- Vehicle context: Skoda Octavia I Estate, 1.6 BFQ petrol, Siemens ECU. [Elektroda, kubas10, post #16657526]
- Symptom cluster: EPC light, power drop, intermittent after start or while driving. [Elektroda, kubas10, post #16654749]
- Power architecture: some actuators get 12V after relays; others use 5V reference, ground, or signal. [Elektroda, sulof1601, post #16654801]
- EGR adaptation was performed after replacement; drivability improved versus prior “tugging.” [Elektroda, kubas10, post #16657108]
- Proven fix in thread: repair chafed wiring harness under the battery tray. [Elektroda, kubas10, post #16680938]
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?
- Read measuring blocks for ECU voltage, EGR, throttle, and MAF.
- Perform EGR adaptation, then recheck live data.
- 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]
