U1688 Smart Auto Trouble Code

U1688 Smart the main thing to check is to verify the operation of the VCT solenoid. You're looking for a sticking or stuck VCt solenoid valve caused by contamination. Refer to vehicle specific repair manual to perform component tests for the VCT unit.

The leak detection pump is part of the evaporative emissions system. This system tests the fuel system to make sure it is not leaking fuel vapors into the air. The system pulls a vacuum on the fuel system and holds it for a period of time.

U1688 Smart Possible Solution:

Brake Switch Out of Self-Test Range Indicates that during Key On Engine Off (KOEO) Self-Test, BPP signal was high. Or during Key On Engine Running (KOER) Self -Test, the BPP signal did not cycle high and low. Open or short in (BPP) circuit Open or short in stoplamp circuits Damaged PCM Malfunction in module(s) connected to BPP circuit (Rear Electronic Module [REM] Windstar and LS6/LS8 and Lighting Control Module (LCM) Continental and Town Car) Damaged Brake Switch Misadjusted Brake Switch Check for proper function of stoplamps. Follow correct Self-Test procedures, refer to Section 2, Quick Test.

Smart U1688 Engine Trouble Code Description For All Models :

U1688 meaning and repair processes are the same for all Smart models.

After understanding U1688 Smart error code for your Smart car, now you can repair yourself.
U1688 Smart Trouble Repair Process:

If your vehicle failed a U1688 Smart test and the U1688 Smart Check Engine Light is NOT on, chances are you have a problem with the OBDII system, a burned out MIL lamp, or a faulty catalytic converter. The converter is essentially an afterburner that cleans up the exhaust after it exits the engine. The OBDII system uses a ownstream oxygen sensor to monitor the efficiency of the converter, and it should detect a drop in converter efficiency if the converter has been contaminated or is failing (ignition misfiring, leaky exhaust valves, and oil burning can all damage the converter). What you want to look any conditions that might cause ignition misfire, an overly rich or lean fuel condition, or loss of compression. Use your OBD Express DIY to look at the oxygen sensor outputs, coolant temperature, airflow, calculated engine load, and inlet air temperature.

On 1999 and later U1688 Smart engines, the instrument cluster has a built-in self-diagnostic mode that can be accessed by pressing and holding the instrument cluster SELECT/RESET button. Insert the ignition key and turn to the RUN position (but don't crank or start engine). Continue to press and hold the SELECT/RESET button (for 5 seconds) until the word TEST is displayed by the odometer. Release the SELECT/RESET button within three seconds after the word TEST is displayed to begin the self-diagnostic mode.

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