QuestionHi HT,
For some time now (about 2 months), I have been experiencing an intermittent start problem with my 2000 Hyundai Sonata, v-6 2.5 litre. Intermittently, the car won't start. It will crank very weakly (like the battery is dead)even though a volt test shows the battery to be putting out 12.9 volts (by the way, the battery is brand new because I thought that was the problem). When I jump the battery, it starts right up. Sometimes it will start fine for a few days before I experience the no start problem again. I thought that it might be a parasitic drain or a voltage drop but the problem occurs whether accessories i.e. radio, heater are left on or turned off upon turning off the car. I used two OBD scan tools, Actron and CarMd, to try to access trouble codes. Actron showed no code but CarMd showed 2 codes, P0711, Transmission Fluid Temperature Sensor A Circuit and P2300, Ingnition Coil "A" Primary Control Circuit Low. Both these codes were deemed intermittent problems discovered by the car's ODB system. Do you think that the ignition coil is the problem, and if so, how would I go about confirming which coil is faulty? If it's not the coil, could it be a starter problem or some other problem that I should be looking into? Keep in mind that whatever the problem is, it's not setting off the check engine light. Any advise on how I should proceed would be greatly appreciated. Thank you.
AnswerYou should examine the connections at the battery, re-examine the battery itself, and check for parasitic draw. The fact that it cranks slowly and starts normally if jumped indicate that you're not getting enough voltage to the starter and that adding jumper cables supplies the required voltage.
When the problem occurs, take the following readings:
-- voltage across battery terminals with car off.
-- voltage across battery posts (the portion that's actually part of the battery) while cranking.
-- voltage across the cable ends while cranking.
-- voltage across the battery terminals with engine running (do this last after jump-starting).
If the first reading is low, you have an indication that the battery is discharged. In this case, check for parasitic draw. To do this, turn all devices on the car off, remove the negative battery cable, and install an ammeter between the negative cable end and the negative battery post. You should have a value of 50mA or less. Values of 200mA or higher can significantly discharge overnight even a new battery.
If both the second and third readings are below about 10V, then you again need to check for why the battery has been discharged. It could be caused by parasitic draw or by a faulty alternator.
If the third reading is significantly less than the second reading, you have poor contact between the cables and the battery.
If the fourth reading is less than 13.5V, your alternator is likely defective.
P2300 is not used on this vehicle, so I suspect there is a communication issue between CarMd and your vehicle. P0711 indeed indicates a problem with the transmission fluid temperature circuit. Since we already have one false code from this reader, the P0711 is in doubt as well. Regardless, even if not false, a faulty fluid temperature sensor or sensor circuit cannot drain the battery and will not make the car difficult to start. It may, on the other hand, cause the transmission to shift abnormally.
