| This guide covers the 8 most reported problems by CNG car owners in India — from the annoying to the genuinely concerning. Each problem has a clear diagnosis and the exact fix, with costs for 2026. |
CNG cars are the most economical fuel option for Indian urban drivers. The running cost advantage over petrol is so significant — Rs. 2.50–3.00 per km versus Rs. 5.50–6.50 per km — that for high-mileage urban drivers, no other fuel choice comes close. But CNG ownership comes with a specific set of problems that petrol car owners never encounter. Most of them are solvable and inexpensive. Knowing what they are before they happen is better than discovering them on a Monday morning with a car that will not start.
Problem 1 – Car Takes Long to Start on CNG in the Morning
This is the most universally reported CNG car complaint in India, particularly in winter or after the car has been parked overnight. The root cause: CNG cars start on petrol and then switch to CNG after the engine reaches operating temperature (typically 1–2 km of driving). If the petrol reserve is very low — less than half a litre — there may not be enough petrol for a clean cold start.
Fix: Always keep at least Rs. 200–300 worth of petrol in the tank alongside your CNG. The CNG-to-petrol switch relies on having adequate petrol for cold starts. This is the single most common cause and the cheapest fix — fill a few hundred rupees of petrol.
Other causes: Dirty or worn spark plugs (CNG burns hotter than petrol and wears plugs faster), weak battery unable to turn the engine over adequately, or a faulty CNG kit pressure regulator that needs adjustment.
Cost to fix: Spark plug replacement: Rs. 600–1,500 for a set | Pressure regulator adjustment: Rs. 300–600 | Battery: Rs. 3,500–5,000 if needed
Problem 2 – Mileage on CNG Has Dropped
A CNG car that used to deliver 28–30 km/kg but now gives 22–24 km/kg has a problem worth diagnosing. CNG mileage deterioration is almost always caused by one of three things:
Dirty injectors or CNG nozzles: The CNG injector nozzles accumulate deposits over time just like petrol injectors. A CNG injector cleaning service (Rs. 1,000–2,000) restores the spray pattern and recovers lost mileage.
Incorrect CNG kit calibration: The CNG ECU controls how much gas is injected. Over time, or after a battery replacement, calibration can drift. A recalibration at a CNG service centre (Rs. 500–1,200) often recovers 2–4 km/kg.
Dirty air filter: Same as petrol cars — a clogged air filter forces rich running and reduces mileage. Replace every 15,000 km (Rs. 300–700).
| 📖 Also Read: How to Increase Car Mileage India 2026 – 12 Tips — General mileage tips that apply to CNG cars as well — tyre pressure and driving style have the same effect https://motorsadda.in/how-to-improve-car-mileage-india-tips-2026/ |
Problem 3 – Power Loss When Switching to CNG
All CNG cars lose some power on CNG versus petrol — this is physics. CNG has lower energy density per unit volume than petrol, so less power is available from the same engine. Factory CNG cars (WagonR, Dzire CNG etc.) are calibrated to minimise this — the loss is typically 8–12% which is barely noticeable in normal driving. If the power loss feels significantly more than this, something is wrong.
Cause: Low CNG cylinder pressure (tank running low), blocked CNG filter, faulty pressure regulator, or CNG kit that needs recalibration. Check the CNG gauge first — if below 20 bar, power will drop noticeably.
Fix: Refill CNG if gauge is low. If pressure is adequate but power is still poor — CNG kit service and recalibration (Rs. 800–1,500).
Problem 4 – Car Refuses to Switch from Petrol to CNG
Modern CNG cars switch automatically to CNG once the engine coolant reaches operating temperature. If the switch does not happen, or the CNG button does not respond, the causes are usually electrical.
- CNG kit wiring issue — a loose connection to the temperature sensor or the CNG switch itself prevents the automatic changeover
- CNG ECU fault — requires diagnostic scan at a CNG service centre (Rs. 500–1,000)
- Low CNG pressure in cylinder — below a minimum pressure, the system will not switch. Check gauge.
- Faulty solenoid valve — the valve that opens the CNG supply is stuck or failed. Replacement: Rs. 1,500–3,500
Problem 5 – Knocking or Pinging Sound on CNG
A knocking or pinging sound from the engine while running on CNG typically indicates the CNG-to-petrol ignition timing has not been correctly calibrated for CNG’s higher octane. CNG has an octane rating of approximately 130 — significantly higher than petrol. An engine tuned purely for petrol ignition timing will be retarded for CNG, causing knock.
Fix: CNG kit ECU must be calibrated specifically for CNG ignition advance. A proper CNG-specific calibration by an authorised CNG service centre. This is why choosing a quality authorised CNG kit installer matters — poor installation often skips this calibration step. Calibration cost: Rs. 800–1,500.
Problem 6 – Smell of Gas Around the Car
Any smell of CNG around a parked or running car is a serious safety issue and requires immediate attention. CNG is lighter than air and dissipates quickly in open areas, so smell indicates an active leak.
What to do immediately: Park in open air, do not start the engine or use any electrical switches, open all windows and doors, move away from the vehicle, and call a CNG service centre or your roadside assistance number. Do not attempt to diagnose or fix a CNG leak yourself.
Common causes: Damaged CNG cylinder valve, loose pipe connection, worn O-ring at the cylinder connection, or a cracked high-pressure pipe.
Cost: Minor connections and O-ring repair: Rs. 500–2,000 | Cylinder valve replacement: Rs. 3,000–8,000 | Never delay this repair
Problem 7 – Annual CNG Cylinder Testing Due
By law, CNG cylinders in Indian vehicles must be tested and certified by a government-authorised facility every 3 years, and replaced every 15 years. This is a legal requirement — driving with an expired cylinder certification is a traffic offence and an insurance coverage issue. Many CNG car owners are unaware of this requirement.
Process: Take the vehicle to a government-authorised CNG testing station (not just any CNG service centre — the testing station must be specifically authorised for cylinder testing). The test involves pressure testing and visual inspection. A certificate is issued if the cylinder passes.
Cost: Rs. 800–1,500 for the test and certification | Rs. 8,000–18,000 for cylinder replacement if required
Problem 8 – Boot Space Insufficient After CNG Installation
This is not a mechanical problem but it is the most commonly complained-about CNG ownership issue. The CNG cylinder in aftermarket conversions is installed in the boot, taking up 40–50% of usable boot space. For factory CNG cars, the cylinder placement is better optimised but still reduces boot space compared to the petrol equivalent.
Workarounds: For factory CNG cars, this is not changeable — it is the design. For aftermarket conversions, a cascaded twin-cylinder setup (two smaller cylinders instead of one large) spreads the load and can preserve more usable boot shape, though total volume loss is similar. A roof carrier or tow bar carrier can partially compensate for regular load-carrying needs.
Frequently Asked Questions
Q: Why does my CNG car not start in the morning in India?
The most common cause is insufficient petrol in the reserve tank. CNG cars start on petrol and switch to CNG after warming up — if petrol is very low (under 0.5 litres), cold starts become unreliable. Always keep Rs. 200–300 of petrol alongside your CNG. If petrol is adequate but starting is still difficult, check spark plugs (worn faster by CNG’s higher combustion temperature) and battery condition.
Q: Is CNG harmful for car engine in India?
Factory-fitted CNG from manufacturers like Maruti, Hyundai, and Tata is engineered for CNG use from the ground up and has no negative impact on engine life. Properly installed aftermarket CNG kits from authorised installers (BRC, Lovato, Landi Renzo) also do not damage engines when the kit is correctly calibrated. Poorly installed or incorrectly calibrated kits can cause valve seat wear from CNG’s dry combustion — this is why authorised installation and proper valve seat hardening are important.
