Erratic operation of ‘Water in fuel filter’ light usually indicates failing battery in Swift (diesel)

A couple of months ago, ‘Water in fuel filter’ light came on (along with SVS light) in my Swift Vdi. I drained the fuel filter but the light kept coming on (and often going off during the next start-stop cycle, only to come on again after a day or two). In other words, this warning light started behaving in an erratic manner and its coming on and going off had nothing to do with presence or absence of water in the fuel filter.

As expected, even on days when the ‘Water in fuel filter’ light did not come on, the SVS light did not go off after 4 seconds of turning on the ignition. This happens because when the ECU detects a fault, the fault code (DTC) is registered in the ECU and the SVS light won’t go off after 4 secs of turning on the ignition unless the DTC code is ‘cancelled’ using the Tech-2 diagnostic tool.

I took the car to MASS where they found the DTC code to be P2264 – ‘Fuel filter water detection sensor circuit’. Since it was already established that the warning light was behaving erratically, the MASS suspected the battery because they had come across many cases of warning light malfunction when battery was weak in diesel Swifts.

Even in this forum diesel Swift owners have reported malfunction of warning lights with a weak battery. Therefore, I decided to thoroughly examine my battery (original Exide DIN 65 MF) before taking the decision to change it. I must mention here that I started experiencing some minor starting problem at this time.

I removed the battery from the car and charged it overnight with my external battery charger. The specific gravity readings were as follows :
Initial sp. gr. 1250 1250 1250 1250 1240 1250
After charging 1280 1270 1280 1270 1260 1280

After overnight charging, all cells were gassing freely, i.e., battery was fully charged. Terminal voltage was 12.85V.

From the specific gravity readings it seemed to me that the battery was okay and I fitted it back in the car. Things worked fine for a few days and thereafter the ‘water in fuel filter’ light started coming on again. Also starting problems increased greatly. On a couple of occasions when the car refused to start after 2-3 attempts, I feared that the car may not start at all, but luckily the car started on the 3rd or 4th attempt. One thing was sure -- something had to be done urgently to prevent getting stranded on the road.

I then got the battery load tested at a battery dealer and when it failed the test, the decision to buy a new battery was obvious.

After substantial research on the internet I decided to go for Base Terminal DIN 66 BT MF. I found that Base Terminal had built a reasonably good reputation in the Indian market, offered 2-year replacement warranty followed by a 2-year pro-rata discount warranty and good value-for-money. I bought this battery (from M/s Moonka Sales, Q-Road, Bistupur, Jamshedpur) for Rs 6800 and received Rs 800 as buy-back for my old Exide – in other words, I had to shell out Rs 6000 only.

After fitting the new battery, I got DTC cancelled at MASS. All problems resolved thereafter.

To summarise :

1) Specific gravity of all cells in a lead-acid battery may be okay but only a load-test can reveal the actual health of the battery. The battery should be able to deliver enough current under full load (during starting) to crank the engine at a high enough RPM to successfully start the engine. This is especially relevant to diesel engines because they have a high compression ratio and the temperature of the compressed air at the end of the compression stroke holds the key to ignition. In other words, it is not enough that the battery is able to crank the engine – the battery should be able to crank the engine at a sufficiently high RPM to initiate ignition of the fuel injected towards the end of the compression stroke.

2) In the 1.3 lit Multijet engine (fitted in diesel Swift and some other Indian cars), the ECU and Sensors seem to be quite sensitive to the battery voltage and tend to malfunction when the battery becomes weak (voltage falls). Erratic and false operation of warning lights, usually the ‘Water in fuel filter’ light, appears to indicate a failing battery.

3) The battery life in a diesel car seems to be significantly less than in a petrol car with comparable BHP. This is mainly due to the fact that a battery is subjected to much more stress every time it starts a diesel engine because diesel engines have a high compression ratio and much more force is required to crank a diesel engine. Furthermore, a petrol engine can start at a lower cranking RPM as compared to a diesel engine and therefore, a battery which is incapable of starting a diesel engine can continue to start an equivalent petrol engine for some more months.

4) The original Exide battery in my Swift Vdi lasted for about 3 ½ years (with no shortcoming in maintenance). Batteries in my earlier petrol cars (Maruti-800, Premier 118NE and Maruti Esteem) used to last for 4 to 5 years.

5) It is perfectly safe to disconnect (or take out) your battery in a diesel Swift for a day or more because the non-volatile memory in the ECU ensures that all essential programming and data for efficient operation of the engine, odometer reading, etc., are retained. Every time you disconnect your battery, you only lose your music system and trip meter settings.

6) Base Terminal seems to be a good value-for-money option to Exide and other leading battery brands in India. However, I would like to give my final verdict only when this new battery dies (if I’m still married to my Swift Vdi then!).