07 Audi Q7 V6 3.6L high pressure fuel rail pressure sensor AUDI Q7 (4LB)

Audi Q7 3.6L Inconsistent Starting: Diagnostic Guidance

Your Audi Q7’s inconsistent starting—cranking but rarely running, with brief sputters—suggests a fuel delivery or electrical issue. Below is a breakdown addressing your specific questions, based on available information and typical layouts for the 4L chassis Q7.

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Low Pressure Fuel Pressure Sensor Location

- The *low pressure fuel pressure sensor* is typically located on or near the fuel filter assembly, which is often accessible under the rear seat, above the fuel tank. The Q7 has fuel pump assemblies on both sides of the tank, accessible by removing the rear seat and lifting the round access covers. The high pressure sensor is on the engine’s fuel rail, but the low pressure sensor is generally integrated with or near the in-tank pump assembly.

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Fuse Carriers Under Dash (Center Dashboard Area)

- The fuse carriers under the dash (often called the “Central Electrical Panel” or “Fuse Panel C”) contain fuses for various systems including the starter circuit, fuel pump, and ignition. For exact fuse numbers and their assignments, refer to the fuse card in your owner’s manual or the panel cover. Commonly, fuses for the starter circuit, fuel pump, and engine management are located here. Unfortunately, the precise fuse numbers for your specific Q7 4L were not provided in the search results; consult the fuse diagram for your model year for exact details.

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Starter Motor Relays (J53 and J695) Location

- Both “Starter Motor Relay-J53” and “Starter Motor Relay 2-J695” are generally housed in the under-hood fuse/relay carrier. In many Audi models, relays are labeled numerically (e.g., #370). These relays control the electrical current to the starter solenoid and motor. The under-hood fuse/relay box is typically on the driver’s side near the firewall. Relays labeled #370 are commonly associated with starter circuits, but always verify with a relay diagram for your specific model year to avoid confusion.

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Terminal 50 (Starter Circuit) Troubleshooting

Terminal 50 is the circuit that activates the starter solenoid when you turn the key or press the start button. If you have a Terminal 50 issue, check:

- The starter motor and its solenoid.
- The wiring from the ignition switch/push start button to the starter relay and then to the starter motor.
- The starter relays (J53, J695).
- The battery and its connections.
- The ground connections (see below).

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Ground Wire Locations (Chassis 4L Q7)

While clear pictures are not available in the search results, typical ground locations on the Q7 4L chassis include:

- Engine Block: Main engine ground strap to chassis (often near the transmission bellhousing).
- Under Dash: Ground points behind the kick panels (driver and passenger side).
- Trunk/Cargo Area: Ground points near the battery or fuse box.
- Front Fenders: Ground points in the engine bay, often near the strut towers.
- Under Seats: Ground studs near seat mounting points for electrical modules.

Check these locations for corrosion, looseness, or damage. Clean and tighten as needed.

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Additional Notes

- If you have a code like P12A2 (high fuel rail pressure sensor issue), address sensor wiring and connectors first.
- If you replaced the in-tank pump or fuel pressure regulator and still have issues, verify both low and high pressure circuits.
- A full diagnostic scan (as you mentioned) will help pinpoint electrical faults across all modules.