I have a KIA Cerato. It has an intermittent fault which is concerning and lately is very prevalent. It first manifested about three years ago with the dealer being unable to identify the fault and was then dormant for about two years

The car seems to lose power although the engine is running and also appears to be stuck in gear. This happens mostly at low speed such as heavy traffic and is therefore dangerous. The fault can sometimes be cleared by switching off the ignition.

Lately the fault has been accompanied by a check engine light which does not extinguish when switching off the ignition. Diagnostics suggested a faulty crankshaft censor and this was replaced but was immediately followed by the check engine light and the same behaviour which became more prevalent. Diagnostics suggested problems with number 3 cylinder and low battery power and at one point it became stuck in park as I attempted to clear the fault in traffic

any suggestions would be welcome as my mechanic is scratching his head and he has plenty of experience with performance engines

Thoughts:

. Remove and fully charge the battery. Clean battery terminals and cable connections with a terminal brush.
. Check the alternator—regulated battery voltage should be 14 to 15 volts. Clean alternator cable connections with abrasive cloth and coat with dielectric grease.
. Clean all grounds and apply dielectric grease.
. Check all under hood and under dash fuses with a test light or multi-meter.
. Replace spark plugs with the exact brand specified in the owner’s manual (no cross-referenced plugs). Examine old plugs for incorrect brand, signs of wear, and fouling.
. Check/replace coil going to cylinder #3.
. Check/replace Transmission Range Sensor (TRS) or Neutral Safety Switch.
. Disconnect the negative battery cable overnight—this will force the PCM to learn all new shift points.

Note: If the CEL stays on, when the ignition switch is turned to on, the PCM may be bad. Before doing anything extreme, disconnect the negative battery cable and clean the PCM ground.