U3858 Diagnostic Trouble Code

U3858 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 U3858 diagnostic trouble code may include:

Carbon Buildup on O2 Sensor
Malfunction Indicator Lamp (MIL) illuminated
Hesitation upon acceleration
Engine surge

Possible Causes :

Rusty exhaust systems, cracked exhaust manifolds or damaged or missing gaskets or donuts will cause air leaks.
An air leak forward of the DPF will change the sensor readings resulting in the code
Some aftermarket accessories and performance modifications

Repair Processes :

Look at the plug wires to make sure they are not burnt or laying on the exhaust. Check to make sure they are not burnt or corroded. If in doubt, get some Electrical Contact cleaner at any parts store if cleaning of the terminals is needed. Find out what kind of system you have and verify that voltage to the fuel level sensor is present at the fuel pump wiring harness.

Process Tips

Diagnostic trouble code U3858 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 U3858.

Fortunately, U3858 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

U3858 Trouble Code For Specific Cars

U3858 Skoda L Knock Sensor 1 Circuit Input Intermittent (Bank 1 or Single Sensor)
U3858 Mercedes Cl 63 ABS Inlet Valve Coil RF Circuit Short To Ground
U3858 Honda Ssm RESCU/VEMS Input Circuit Short to Battery
U3858 Mg Rv12 Air Temperature Internal Sensor Circuit Failure
U3858 Bmw Serie 2 Active Tourer Clutch Position Sensor Circuit Intermittent Malfunction
U3858 Ghia 450 Oil Change Reset Button Circuit Open
U3858 Riley Elf Horn Relay Coil Circuit Short to Vbatt