Code
P1685
FIAT
P — Powertrain
Motorised throttle without learned values
Views:
UK: 18
EN: 30
RU: 21
AI status
Completed
Completed
100%
Causes
- Battery disconnected, low battery voltage or recent battery replacement/voltage loss
- Throttle body removed, replaced or cleaned without performing learn/adaptation
- Failed or intermittent throttle position sensor(s) or throttle actuator motor
- Damaged wiring, poor connector contacts or corrosion on throttle harness
- ECU software fault or lost calibration memory
- Mechanical binding or contamination in the throttle plate/linkage
Symptoms
- Check Engine Light (MIL) illuminated
- Reduced engine power / limp-home mode or limited throttle response
- Engine may not idle correctly, stalling or high/erratic idle
- Throttle pedal has delayed or inconsistent response
- Diagnostic trouble code P1685 (or manufacturer-specific message) present
- Vehicle may require a throttle relearn/adaptation procedure to restore normal operation
What to check
- Read and record all stored DTCs and freeze-frame data with a diagnostic scanner
- Verify battery voltage and charging system health (battery > 12 V, charging nominal)
- Inspect throttle body connector and wiring for damage, corrosion, loose pins
- Visually inspect throttle plate for carbon buildup or mechanical obstruction
- Check fuses and relays related to throttle and ECU power circuits
- Using a scan tool, view real-time throttle position, commanded throttle, and actuator status
Signal parameters
- Closed throttle TPS voltage: typically ~0.2–1.0 V (manufacturer-specific)
- Wide open TPS voltage: typically ~4.0–4.9 V (manufacturer-specific)
- Commanded throttle angle/percent (0–100%) from ECU
- Actual throttle angle/percent reported by throttle body
- Throttle actuator current or duty cycle when moving
- Battery voltage during key-on and crank conditions
Diagnostic algorithm
- Connect a capable scan tool. Read and save all DTCs and freeze-frame data. Note any other related codes.
- Verify battery voltage and charging system. Recharge or replace a weak battery and clear codes if battery was low/disconnected.
- Visually inspect throttle body and harness connectors. Repair any damaged wires or corroded terminals.
- Check for mechanical binding or heavy carbon buildup on the throttle plate; clean if required and verify free movement.
- With the scan tool, monitor actual vs commanded throttle position and TPS voltages while operating the throttle. Look for inconsistent readings or failure to move.
- Perform continuity/resistance checks on throttle motor and TPS circuits per manufacturer specifications. Repair or replace wiring/components that fail.
- If hardware is serviceable and checks okay, perform the factory throttle adaptation/learn procedure (follow Fiat service manual steps exactly).
- Clear codes and retest. If P1685 returns and hardware checks fail, replace the throttle body assembly. If code persists after replacement and correct adaptation, consider ECU/software reflash or replacement.
- After repair, confirm normal idle, throttle response, and that no related DTCs remain stored.
Likely causes
- Battery was recently disconnected or drained and the ECU lost learned values
- Throttle body was replaced or removed and adaptation was not performed
- Faulty throttle position sensor(s) giving incorrect voltage/values
- Throttle actuator motor or its driver circuit is defective or has an open/short
- Corroded connector or broken wire at the throttle body harness
Fault status
Status
Motorised throttle without learned values — throttle control module reports no stored calibration/adaptation for the electronic throttle. Throttle adaptation required or component malfunction.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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