17705 – Connection charger-throttle valve pressure drop (Audi)

Audi-specific code — factory diagnostic data

17705 means the Audi engine computer sees an abnormal pressure drop in the air path between the turbocharger outlet and the throttle valve. In plain terms, the engine may lose boost, feel weak, hesitate, or run unevenly under load. This is a manufacturer-specific Audi code, not a universal SAE meaning. According to Audi factory diagnostic data, this code indicates Connection charger-throttle valve pressure drop. On an Audi TT, that points to the pressurized intake tract and its related control hardware. The code identifies a suspected trouble area only. It does not prove that any single hose, valve, sensor, or turbocharger part has failed.

17705 Quick Answer

17705 tells you the Audi ECM detected too much pressure loss between the charger and the throttle valve. Most often, the cause is a boost leak, loose connection, split hose, or a control problem that prevents the intake tract from holding expected pressure.

What Does 17705 Mean?

The official Audi definition is Connection charger-throttle valve pressure drop. That means 01-Engine Control Module 1 detected that the boosted air path from the charger to the throttle body did not maintain pressure as expected. In practice, the engine loses some of the compressed air before it reaches the intake manifold, so power drops and fuel control can become less stable.

For diagnosis, separate the message from the cause. The code describes a pressure-loss condition, not a failed part. The module compares air charge behavior to expected operating conditions using its available load and pressure inputs. If the measured result shows an excessive drop in the connection between the charger and throttle valve, the ECM sets 17705. That matters because the fault can come from the plumbing, the sealing surfaces, the throttle body connection, the boost control system, or even a sensor input issue that makes the pressure model inaccurate.

Theory of Operation

Under normal operation, the charger compresses intake air and sends it through the pressure side of the induction system to the throttle valve. The Audi ECM manages load by coordinating boost control, throttle angle, and fuel delivery. The air path between those points must stay sealed so the commanded charge pressure actually reaches the engine.

This code appears when that sealed path no longer behaves correctly. A hose can split, a clamp can loosen, an intercooler can crack, or a connection near the throttle valve can leak under boost. The same symptom can also develop if the boost control system overworks or under-controls the charger, or if a related pressure signal misleads the module. That is why you confirm the leak or control fault with testing before you replace parts.

Symptoms

Drivers and technicians usually notice boost-related performance problems first.

• Warning light: The malfunction indicator lamp turns on and stores 17705 in the engine module.
• Low power: The Audi TT feels flat during acceleration, especially when boost should build.
• Hesitation: Throttle response becomes soft or uneven when the engine transitions into load.
• Limp mode: The ECM may limit performance to protect the engine and control emissions.
• Whooshing noise: Escaping charge air may create a hiss or rush sound from the turbo plumbing.
• Rough running: Airflow errors can upset load calculation and cause unstable running under boost.
• Poor fuel economy: The engine may use more fuel because requested load and delivered air no longer match.

Common Causes

• Charge pipe or boost hose leak: A split hose, loose clamp, or poor seal between the charger and throttle valve lets pressure escape and creates the pressure drop the Audi engine module detects.
• Disconnected or misrouted intake plumbing: A hose installed on the wrong port or left partially off after service changes the measured pressure behavior in the connection path.
• Cracked intercooler end tank or core: Damage in the boosted air path leaks charge pressure before it reaches the throttle valve and can set this manufacturer-specific Audi fault.
• Throttle body sealing problem: A damaged throttle body gasket or poor throttle housing fit can leak pressurized air at the final section of the charger-to-throttle connection.
• Boost pressure sensor reading error: A biased or unstable pressure signal can make 01-Engine Control Module 1 calculate an abnormal pressure drop even when the plumbing holds pressure.
• Wiring or connector fault in the pressure sensing circuit: Corrosion, spread terminals, or harness damage can distort the pressure input the module uses to judge pressure drop.
• Restriction in the charge air tract: An internal hose collapse, debris, or intercooler blockage can create an actual pressure loss between the charger outlet and the throttle valve.
• Aftermarket or incorrectly fitted intake components: Nonstandard pipes, couplers, or clamps often disturb sealing and sensor relationships on the Audi TT charge-air system.

Diagnosis Steps

You need a capable scan tool, service information, a smoke machine or boost leak tester, a digital multimeter, and basic hand tools. Use the scan tool to read fault status and data first. Then test the charge-air path and related circuits in a logical order. Do not replace the throttle body, sensors, or hoses until testing proves the fault.

1. Confirm 17705 in 01-Engine Control Module 1. Record stored, pending, and confirmed fault status. Save freeze frame data, especially battery voltage and ignition state. Freeze frame shows the exact conditions when the code set. If the issue acts up only during a road test, use a scan-tool snapshot to capture live pressure behavior at that moment. A pending code may reflect one trip only, while a hard circuit-related fault often returns quickly.
2. Check related fuses and power distribution first. Inspect the full charger-to-throttle circuit path before any meter work. Look for loose boost hoses, oil tracks at joints, missing clamps, cracked plastic pipes, damaged intercooler tanks, and signs of recent intake service on the Audi TT.
3. Verify engine control module power and ground under load before deeper circuit checks. Use voltage-drop testing with the circuit operating, not continuity alone. Ground drop should stay below 0.1 volt under load. High resistance can pass a simple voltage check and still upset sensor calculations.
4. Inspect connectors and harness routing at the boost pressure sensor, throttle body area, and any nearby intake pressure-related components. Check for backed-out terminals, corrosion, damaged locks, harness rub-through, and oil contamination. Tug lightly on each wire near the connector to catch broken conductors inside the insulation.
5. Use the scan tool to review live data for the pressure input the module uses for this fault. Compare key-on engine-off readings to expected ambient behavior and then compare idle and light-load response. If the signal looks biased, erratic, or implausible, move to circuit testing before condemning the sensor.
6. Pressure-test or smoke-test the complete charge-air tract from the charger outlet to the throttle valve. Watch every coupler, clamp seat, intercooler seam, and throttle body connection. A small leak often shows up as smoke or faint hissing long before it becomes obvious in normal visual inspection.
7. If the plumbing passes the leak test, perform sensor circuit checks with service information in hand. Verify reference supply, ground quality, and signal integrity at the sensor connector. Do not rely on resistance checks alone. Confirm the signal changes smoothly and matches actual pressure conditions.
8. Inspect the throttle body mounting and sealing surfaces. Check for gasket damage, housing misalignment, or evidence that the throttle body was removed and not seated correctly. On some Audi layouts, a leak at this point creates a pressure drop fault without setting a separate throttle actuator code.
9. If live data and leak testing suggest a flow restriction instead of a leak, inspect the intercooler and connecting hoses for internal collapse, debris, or obstruction. Flex suspect hoses by hand and inspect inside where possible. A restriction can produce a real pressure loss across the connection.
10. After repairs, clear the code and repeat the operating conditions that originally set it. Recheck live data and make sure 17705 stays out of pending and confirmed status. Review readiness and rescan the Audi TT after the drive cycle to confirm the repair holds.

Professional tip: This code points to a suspected trouble area, not a failed part. On Audi systems, the fastest wrong answer is a throttle body or sensor swap. First prove whether the pressure drop is real with a smoke or pressure test. Then prove the pressure signal is accurate with circuit testing. That order prevents expensive mistakes.

Possible Fixes

• Reseal or replace leaking charge-air hoses and clamps: Fix split couplers, loose clamps, and poor joints only after leak testing identifies the exact source.
• Repair damaged intercooler or charge piping: Replace cracked plastic pipes or leaking intercooler components when testing confirms pressure loss in that section.
• Correct intake plumbing installation errors: Refit any misrouted, loose, or partially seated hoses and verify proper clamp engagement across the full charger-to-throttle path.
• Repair the pressure sensor circuit: Fix corroded terminals, damaged wiring, poor grounds, or reference feed faults when circuit tests show signal problems.
• Restore proper throttle body sealing: Replace the gasket or correct mounting issues if testing shows leakage at the throttle body connection.
• Replace a biased pressure sensor only after verification: Install a new sensor only when live data, reference checks, ground tests, and signal testing prove the sensor reports incorrectly.

Can I Still Drive With 17705?

You can usually drive an Audi TT with 17705 for a short distance if the engine runs normally and boost control feels stable. This code points to a pressure drop in the connection between the charger and throttle valve, so drivability can change quickly under load. If you notice low power, surging, hissing, limp mode, stalling, or a flashing warning lamp, stop pushing the car and diagnose it first. A boost leak can make the engine run poorly and can force the 01-Engine Control Module 1 to limit performance. Short, gentle trips to a repair location are one thing. Continued hard driving is not smart until you confirm the leak path, hose condition, and sensor plausibility.

How Serious Is This Code?

17705 ranges from a nuisance fault to a clear drivability problem. In mild cases, the Audi only shows a warning lamp and a small drop in performance. That usually happens when a hose connection seeps under boost but seals well enough at light throttle. The situation becomes more serious when the pressure drop grows large enough to upset air charge control. Then the TT may hesitate, fall into reduced-power operation, or run poorly during acceleration. This code does not automatically prove a failed turbocharger or throttle body. It tells you the module sees a problem area in the charge-air path. Treat it as important because unmetered air loss can affect fuel control, boost regulation, and catalyst protection strategies.

Common Misdiagnoses

Technicians often replace the turbocharger, diverter valve, throttle body, or charge sensor too early. The wording of this Audi code pushes people toward parts instead of testing. The usual miss is a simple leak at a hose joint, intercooler end tank, clamp, split pressure pipe, or damaged seal ring between the charger outlet and throttle valve path. Another mistake comes from ignoring subtype information. The reported FTB suffix -035 is diagnostic subtype data only, not a part name. Shops also skip live-data comparison and never verify requested versus actual charge pressure during the same operating conditions. That wastes money fast. The fix starts with a full visual check, smoke or pressure testing of the boost tract, connector inspection, and scan-tool confirmation before any component replacement.

Most Likely Fix

The most common confirmed repair is sealing the charge-air tract between the turbocharger outlet and the throttle valve. On many Audi applications, that means correcting a loose connection, replacing a split hose, repairing an intercooler or pipe leak, or installing the correct seal at a joint that leaks only under boost. A second common repair path involves restoring accurate pressure feedback after you verify wiring integrity and connector condition at the relevant pressure sensing points. Do not call either repair certain until you duplicate the fault, test the system under load, and confirm that requested and measured pressure values track correctly through a complete drive cycle. Monitor enable conditions vary, so use service information to confirm when the fault check runs.

Repair Costs

Repair cost depends on whether the fault is a boost pressure sensor, charge pipe, intercooler hose, wastegate, or turbocharger itself. Start with visible charge pipe and clamp inspection before assuming the turbocharger has failed.