Experiencing a check engine light in your Volkswagen can be unsettling. Recently, while leaving the in-laws, my Jetta illuminated the dreaded check engine light, signaling an engine problem. After a few days of cautious driving and listening for any unusual noises, I finally got my hands on a VAGCOM tool to diagnose the issue. The scan revealed two Vw Codes: 17058 and 17911. While familiar with the glow plug fault (17058), the second code, 17911 (P1503), related to the alternator load signal, was a new challenge. After some digging and research within the TDIclub community, I pieced together a solution and want to share it with fellow VW owners.
Understanding VW Code 17911 (P1503): Implausible Alternator Load Signal
VW code 17911, also known as P1503, indicates “Load Signal From Alternator Term. DF: Implausible Signal.” This vw code doesn’t typically trigger the check engine light itself; in my case, the glow plug fault was responsible for that. However, code 17911 was consistently stored in the system. Despite clearing the code multiple times, it reappeared daily after my commute. This persistent recurrence pointed to an underlying issue that needed addressing.
Root Cause: The Short Harness Problem
The root cause of this vw code often lies in a seemingly minor, yet critical, design flaw: a slightly too-short wiring harness. Located at the front of the engine, this harness connects the alternator, voltage regulator, and A/C compressor (if equipped) to the main wiring harness beneath the battery box. A four-pin connector (or two-pin in models without A/C) situated near the starter becomes the point of stress due to this insufficient length.
Within this harness are five wires, each serving a specific function:
- A thick red power wire carrying the alternator’s output to the battery’s fuse panel.
- A green and black wire for the A/C compressor clutch.
- A brown and black wire, also for the A/C compressor clutch.
- A very thin brown and red wire from the voltage regulator to the Engine Control Module (ECM).
- A very thin blue wire from the voltage regulator, connecting to the ECM, the generator indicator light on the dashboard, and the warning chime.
In my case, the critical brown and red wire (number 4) was completely severed. Wires 5 and 3 also showed significant damage, with cracked sheathing and frayed wires, all concentrated near the connector. This physical damage to the wiring is the culprit behind the “implausible signal” and the stored vw code 17911.
DIY Repair Guide: Fixing the Harness
To address this vw code, a hands-on repair is necessary. The first step involves accessing and removing the faulty harness. This requires disconnecting the battery and removing the battery box, air cleaner assembly, and engine cover to gain sufficient access to the harness and its connection points.
Once removed, the damage becomes apparent, typically within a quarter-inch of the connector. Two repair approaches are possible:
- Disassembling the connector, lengthening the wires, and reassembling.
- Removing the connector entirely, lengthening the wires, and creating a permanent, direct connection.
Due to the difficulty in disassembling the connector (it doesn’t seem designed for servicing) and its non-essential nature, I opted for the second method – connector removal.
The repair process then involves:
- Soldering the wires: Carefully cut back the damaged sections of wire. Solder new wire extensions (16 gauge wire is suitable) to each of the five wires, ensuring strong and clean connections.
- Insulating the connections: Use heat shrink tubing to thoroughly insulate each soldered joint, protecting them from the elements and preventing shorts.
- Adding wire loom: Encase the repaired section of the harness in wire loom to provide additional protection and maintain a factory-like appearance.
After completing the wiring repairs, carefully reinstall the harness, ensuring all connections are secure. Reassemble the removed components (air cleaner, battery box, etc.). Finally, reconnect the battery.
Verification and Further Implications
Start the engine and monitor for any warning lights. Take the vehicle for a test drive, keeping an eye out for any issues. Upon returning, use a VAGCOM or similar diagnostic tool to check for stored vw codes. In my case, the repair was successful, and code 17911 was no longer present.
Interestingly, I had also been experiencing frequent taillight, headlight, and brake light failures. I suspect the disconnected wire might have been intermittently contacting other wires within the damaged connector, potentially affecting the electrical system and contributing to these bulb failures. While not definitively proven, resolving the harness issue might also address these related electrical problems.
Conclusion
Encountering vw code 17911 (P1503) can be perplexing, as it doesn’t always trigger a check engine light. However, its persistent presence signals an issue that should be addressed. This DIY guide outlines the common cause – a short wiring harness – and provides a step-by-step repair solution. By addressing this seemingly small wiring flaw, you can resolve the “implausible alternator load signal” error, ensuring the electrical system in your VW operates correctly.
