U1990 Diagnostic Trouble Code

U1990 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 U1990 diagnostic trouble code may include:

Engine surge
Blown fuse (if applicable)
Lack of power
Cherry red hot catalytic converter

Possible Causes :

Rarely - faulty Powertrain Control Module (PCM-programming required after replacement)
Rough running engine due to misfiring plugs. Many engines have misfire codes to indicate the cylinder effected, such as P0307 for number 7.
A large vacuum leak would cause a massive amount of un-metered air to enter the intake manifold resulting in an overly lean mixture.

Repair Processes :

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. It should be pretty close to battery voltage (12 volts). If not, then this is the circuit that has the problem. Replace the oxygen sensor that is downstream from the catalytic converter on the side of the engine that does not contain cylinder #1. Also, if a oxygen sensor code stating "heater circuit malfunction" the sensor has most probably failed.

Process Tips

Diagnostic trouble code U1990 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 U1990.

Fortunately, U1990 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

U1990 Trouble Code For Specific Cars

U1990 Citroen Ami Fog Lamp Switch Failure
U1990 Gaz 34 O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 1)
U1990 Mazda R
U1990 Autobianchi Primula Aux Heater Flame Out Fault
U1990 Alvis Tc Air Suspension Compressor Relay Circuit Short To Battery
U1990 Fairthorpe Tx Injector Circuit Malfunction - Cylinder 7
U1990 Morris Isis Brake Pressure Switch Input Circuit Failure