B1257 Diagnostic Trouble Code

B1257 is a kind of OBD-II Diagnostic B-Body 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 B1257 diagnostic trouble code may include:

Faulty or damaged wiring
The engine oil will exhibit dilution from the ECUs attempts to increase engine temperature. Some vehicles advance the fuel injection timing slightly after top center to afterburn a small amount of fuel to increase exhaust temperatures. Some of this fuel enters the crankcase. When the ECU determines the necessity to regenerate the DPF, the service life of the oil be shortened significantly
Poor fuel economy
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.
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 :

Pack the connector cavity with dielectric silicone compound (same stuff they use for light bulb sockets and spark plug wires) and reassemble. 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.

Process Tips

Diagnostic trouble code B1257 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 B1257.

Fortunately, B1257 is a fairly common OBD code, meaning that it applies to all makes and models of vehicles made after 1996.

B1257 Trouble Code For Specific Cars

B1257 Innocenti Elba SCP (J1850) Invalid or Missing Data for Ignition Switch / Starter
B1257 Citroen C3 Ii Front Wiper Select Switch "B" Short to Ground
B1257 Ferrari Rossa Key Off Voltage Low
B1257 Standard Vanguard Lamp Keypad Output Short Circuit To Battery
B1257 Tata Estate Mirror Passenger Up/Down Motor Stalled
B1257 Mitsubishi Challenger Audio Rear Integrated Control Panel Unit is Not Responding
B1257 Fairthorpe Em Injector Circuit Malfunction - Cylinder 4