P1645 Code: Meaning, Symptoms, Causes & Fix

Overview

Code P1645 indicates a fault in Fuel Pump Resistor Switch Circuit Malfunction, typically within fuel delivery and pressure control.

Symptoms

reduced fuel economy
hesitation under acceleration
engine may stall at idle

Common causes

Disconnected or loose connector affecting fuel pump resistor switch circuit malfunction
Broken terminal inside harness
Connector pin damage/corrosion or harness stress near related components

How to diagnose P1645

Confirm P1645 and capture freeze-frame data with a professional scan tool.
Inspect wiring, connectors, and grounds related to fuel pump resistor switch circuit malfunction for obvious defects.
Use a continuity test from module pin to component to identify opens/high resistance.
Check for related DTCs to identify the root-cause chain before replacing parts.
After repair, clear codes and confirm readiness monitors complete without recurrence.

Severity of code P1645

Moderate: This code is moderate severity: the vehicle may still operate, but fault progression can increase repair cost over time.

Can you drive with P1645?

Most vehicles can be driven short-term with P1645, but postpone heavy load/highway driving until repaired.

If the warning lamp is flashing or drivability/safety is affected, avoid driving and diagnose immediately.

How to fix it (step-by-step)

Repair obvious wiring/connector faults first to prevent repeat parts replacement.
Address the root fault mode (open) in the fuel pump resistor switch circuit malfunction circuit/system.
Apply the required relearn/adaptation procedure if specified by service information.
Road-test and verify P1645 remains cleared under the conditions that originally set the code.

Fix options

Clear corrosion and protect terminals.
Restore continuity and verify pin tension.
Clear DTCs and verify with live data and completed drive cycle.

Typical repair cost

$220-$1100

Common mistakes when diagnosing P1645

Replacing parts without verifying voltage, ground, and signal integrity first.
Ignoring related stored/pending codes that indicate upstream faults.
Skipping post-repair verification drive cycle and readiness checks.

P1645 in common vehicles

P1645 appears across makes such as Nissan, Hyundai, Kia, Volkswagen. Failure patterns differ by platform: wiring routes, software calibration, and component supplier revisions can change root cause.

Frequently asked questions

What causes P1645?

P1645 is commonly set by open faults affecting fuel pump resistor switch circuit malfunction.

How much does it cost to fix P1645?

For P1645, repair costs are typically $220-$1100 depending on exact root cause, labor rates, and part quality.

Can I clear P1645 without repair?

You can clear P1645 temporarily, but the code usually returns until the underlying fault is corrected.