U3990 Lexus Lf Diagnostic Trouble Code

U3990 Lexus Lf code definition:
U3990 is a kind of OBD-II Diagnostic U-Network Diagnostic Trouble Code for Lexus Lf.

U3990 Lexus Lf is triggered when the bank 1 camshaft position sensor doesn't match the signal from the crankshaft position sensor. So if the problem persists despite of your diagnosis, then you should never hesitate to take your vehicle to your dealer or to a qualified mechanic.

Symptoms

Symptoms of a U3990 Lexus Lf diagnostic trouble code may include:

Hesitation upon acceleration
Excessive exhaust leak
Rich or lean exhaust
Lack of power

Possible Causes :

Faulty IMRC actuator relay (if equipped)
A large air leak at or near the number one oxygen sensor would also cause a lean mixture.
Some aftermarket accessories and performance modifications

Common Misdiagnoses

Crankshaft Position Sensor Circuit Performance Problem
TP Sensor Learn Not Complete Problem
Low Coolant Circuit Problem
Cruise Control System - Vehicle Accel Too High Problem
Kick-Down Switch Failed Short Problem

Repair Processes :

It should be pretty close to battery voltage (12 volts). If not, then this is the circuit that has the problem. With the valve disconnected, the red voltmeter lead should be attached to the IMRC valve power wire and the black voltmeter lead connected to ground.

Process Tips

Diagnostic trouble code U3990 Lexus Lf is not difficult to diagnose and repair. Thus, it always pays to have a qualified technician to look after your vehicle should this error code arise.

Diagnosing this code requires the engine to be in good running shape, without unmetered air entering the engine. If other codes that relates to misfiring condition, lean running or air entering the engine is present, then you must first fix those error codes before U3990 Lexus Lf.

Fortunately, U3990 Lexus Lf is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.