2021 Audi V8 TFSI Red Coolant Warning Lamp TSB

Symptoms

Owners of affected Audi V8 TFSI models may observe a critical warning in their instrument cluster. The primary symptom is the illumination of the "Red coolant warning lamp is illuminated in the instrument cluster". This light indicates a potential issue with the vehicle's cooling system, which can lead to engine overheating if not addressed.

Fault Codes / DTCs

When the red coolant warning lamp appears, the engine control module (ECM), identified as J623 (address word 0001), may store one or more of the following diagnostic trouble codes (DTCs):

Code	Description
P218100	Malfunction in cooling system
P017B00	Cylinder head temperature sensor implausible signal
P017C00	Cylinder head temperature sensor short circuit to ground
P017E00	Cylinder head temperature sensor open circuit/loose contact

These codes specifically point to issues with the cylinder head temperature sensor, indicating either a general malfunction, an implausible signal, a short circuit, or an open circuit/loose contact.

Diagnosis and Technical Background

The root cause for the 2021 Audi Q8 red coolant warning lamp and associated DTCs is often traced to the coolant temperature sender G407. Damage to the O-ring of this sensor can allow water to intrude into its plastic housing. This moisture can then damage the sensor element itself, leading to sporadic or consistent malfunctions. This issue can result in the various fault codes listed above, all stemming from the sensor providing incorrect or no data to the ECM.

Technicians will typically begin diagnosis by working through Guided Fault Finding procedures. A crucial step involves visually inspecting the O-ring on the coolant temperature sender G407 for any signs of damage or pinching. This visual check helps confirm if moisture intrusion is the likely cause of the sensor's failure.

Repair Procedure Summary

If the O-ring on the coolant temperature sender G407 is found to be damaged or pinched, the repair involves replacing the G407 sensor. This procedure ensures that a properly sealed and functioning sensor is installed, resolving the issue of water intrusion and restoring accurate temperature readings to the ECM. After replacement, further diagnostic checks and road tests are typically performed to confirm the repair's effectiveness and ensure no further fault codes are present.

Required Tools and Parts

For this repair, technicians will need access to specific diagnostic equipment and parts:

• Diagnostic Tools: VAS 6160 and VAS 6150 testers, running the current version of ODIS (Windows 10), are required for Guided Fault Finding and post-repair checks.
• Parts:
  • Coolant temperature sender G407 (Quantity: 1). Specific part numbers should be referenced in ETKA (Electronic Parts Catalog).
  • Fasteners, bolts, nuts, and screws as needed, per the repair manual (also referenced in ETKA/ELSA).

Warranty Information and Important Warnings

This Technical Service Bulletin (TSB 2062951/1) outlines warranty coverage for the repair. For new vehicles, the repair is covered up to 48 months or 50,000 miles, whichever comes first. For Audi Certified Pre-Owned (CPO) vehicles, the claim type is G10, and owner verification is required. It is important to note that if your vehicle is outside of any applicable warranty, this Technical Service Bulletin is for informational purposes only, meaning the repair costs would be the owner's responsibility.

NHTSA ID: 10193039