U3986 Diagnostic Trouble Code

U3986 is a kind of OBD-II Diagnostic U-Network Diagnostic Trouble Code.

It is considered generic because it applies to all makes and models of vehicles, although specific repair steps may be different depending on your car model.

Symptoms

Symptoms of a U3986 diagnostic trouble code may include:

Blown fuse (if applicable)
Engine surge
Reduction in engine performance, especially at low RPM levels
The light may stay on or light intermittently as the DPF regenerates. The engine will be sluggish on acceleration.

Possible Causes :

An air leak forward of the DPF will change the sensor readings resulting in the code
Rusty exhaust systems, cracked exhaust manifolds or damaged or missing gaskets or donuts will cause air leaks.
Dirty air cleaner element Damaged DPF

Repair Processes :

It should be pretty close to battery voltage (12 volts). If not, then this is the circuit that has the problem. Look for missing ground strap or a rusty ground where the fuel tank is grounded to the frame. Check for damage to the wiring harness connector. Oxygen sensors signal the engine management computer the amount of oxygen present in the exhaust, which is used in determining and controlling the fuel ratio.

Process Tips

Diagnostic trouble code U3986 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 U3986.

Fortunately, U3986 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

U3986 Trouble Code For Specific Cars

U3986 Pontiac Pathfinder Fan Secondary High With Fan(s) Off
U3986 Subaru Legacy 4 Left Rear Turn Lamp Circuit Failure
U3986 Fairthorpe Em Injector Circuit Malfunction - Cylinder 4
U3986 Toyota Super Passenger Door Disarm Switch ckt Short to Ground
U3986 Shelby Super Cars Aero Intake Air Temperature Circuit Intermittent
U3986 Dixi T Idle Air Control Circuit Malfunction
U3986 Goggomobil Fleetwing Parklamp Output Relay Dirver Short to Battery