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Honda Civic GX (CNG Vehicle) with P0170 Fuel Trim Error - 212K Miles, Poor Idle After Injector Rebuild

Model: Honda Civic GX Fault Code: P0170 Posted: 2012-01-22 13:43

My Honda Civic GX has 212,000 miles and recently began sputtering before failing to start. The dealer provided several diagnostic codes: - P0301–P0304: Misfire detected in cylinders 1–4 - P0131: Oxygen sensor failure (front O2 sensor) - P0170: Fuel trim out of specification (Bank 1, as reported by Actron scanner) I have already replaced all four fuel injectors and installed a new front oxygen sensor. Additionally, I replaced the exhaust system and catalytic converter due to a manifold crack. The car now starts but idles poorly and exhibits roughness under light load. The P0170 code persists despite these repairs. What steps should I take next to resolve this issue? Is it related to fuel pressure, sensor calibration, or another component specific to CNG-powered vehicles? I'm seeking advice on troubleshooting the P0170 error in a Honda Civic GX running on natural gas (CNG), especially given its high mileage and the fact that it's not a common vehicle type.

Related fault codes
P0170
Comments (7)
Anonymous 2012-01-23 06:21

Check fuel pressure — ensure it's within the manufacturer-specified range for CNG vehicles. This is often a key factor in P0170 errors.

Anonymous 2012-01-24 01:25

Fuel pressure should be measured using a dedicated gauge. For a Honda Civic GX running on CNG, typical operating ranges are around 35–45 psi depending on engine load and temperature. If pressure is low or inconsistent, it may cause fuel trim errors like P0170. Adjusting fuel pressure usually requires professional tools and calibration — but verifying the baseline first is essential. I'm new to CNG vehicles too, so any detailed guidance would be appreciated.

Anonymous 2012-01-24 06:09

Do you have access to a service manual for your specific Honda Civic GX model? A repair manual with CNG-specific sections would help identify correct procedures and component tolerances.

Anonymous 2012-01-24 21:46

I purchased the car about three months ago with 212K miles. The original Honda inspection recommended only valve adjustments, which were completed. When it failed several months later, I had it towed to a dealer who diagnosed one failing injector — they claimed others were likely compromised and suggested $600 per injector replacement. I declined and instead rebuilt all four injectors for under $300. Now, after online research, I'm relying on community input like this forum. I'll purchase a repair manual soon, but any immediate advice on resolving P0170 would be greatly appreciated.

Anonymous 2012-01-24 21:51

My timeline is off — I bought the car about five months ago and it started acting up four months later. It has been sitting for one month while waiting for a final fix.

Anonymous 2012-01-25 06:03

Are there any auto parts stores near you that can lend or sell a fuel pressure gauge? Do you have access to a scan tool capable of graphing fuel trims and O2 sensor response curves? Is your Civic GX running exclusively on CNG, or does it switch between gasoline and natural gas? If it runs solely on CNG, specialized components and tools may be required — as CNG vehicles often differ from dual-fuel setups. This is a rare vehicle type, so detailed technical insights are especially valuable.

Anonymous 2012-10-13 07:44

Was the replacement oxygen sensor provided by the dealer (Denso) or an aftermarket brand? I noticed this thread may be outdated — if it's been inactive for some time, it might not reflect current CNG vehicle troubleshooting best practices.