A backfire can sometimes cause damage to oxygen sensors (O2 sensors), a critical part of the OBD2 system. While not always the case, a significant backfire can generate excessive heat and pressure that might overwhelm the sensor, potentially leading to its malfunction or failure.
High fuel trims, like +23% on bank 1 and +8% on bank 2 as in one example, indicate the engine computer is compensating for a lean fuel mixture. This lean condition can be a precursor to misfires, which in turn can cause backfires. While misfires can make the oxygen sensor read lean, a lean air-fuel ratio itself can also cause misfires. It’s a cyclical problem.
Before assuming a faulty oxygen sensor, it’s crucial to investigate further. Examining the voltage output from the upstream oxygen sensors (B1S1 and B2S1) is a good starting point. At idle, with a fully warmed engine, these sensors should fluctuate between 0.1 and 0.8 volts. A constant reading of around 0.5 volts suggests a problem with the sensor or its heater circuit. Testing at higher RPMs (2500-3000) can further confirm sensor activity.
A low voltage reading (below 0.5V) from either upstream sensor can be further tested by quickly fluttering the throttle. This action should briefly enrich the fuel mixture, causing the voltage to rise towards 0.9V. If there’s no response, the sensor might be compromised.
Although less likely, a faulty Mass Air Flow (MAF) sensor can also contribute to fueling issues. Disconnecting the MAF sensor temporarily can help determine if it’s playing a role in the problem. However, keep in mind that a clean OEM air filter and properly connected air intake tube are essential for accurate MAF readings and proper fueling, especially in MAF-equipped engines.
While a backfire can potentially damage OBD2 sensors like the oxygen sensor, it’s important to systematically diagnose the root cause of the backfire and the lean fuel condition before replacing parts. Checking fuel trims, examining oxygen sensor voltage outputs, and verifying MAF sensor functionality are critical steps in pinpointing the problem and ensuring a proper repair.
