2003 Silverado Continuously Displays P0155 and P0154 OBD2 Codes After Multiple Sensor Replacements

The P0155 and P0154 codes both refer to the same sensor: Bank 2 Sensor 1 (B2S1). To diagnose: - Check for a 12V supply on the pink wire at the sensor. - Confirm that the black wire has a solid ground connection. - Describe the exact location of the replaced sensor—especially whether it's on the passenger side, as this is critical. - Did you install an aftermarket or OEM O2 sensor? If aftermarket, verify wiring compatibility. - Do you have access to an OBD2 scanner with live data streaming capability? This is essential for accurate diagnosis.

Always use original equipment manufacturer (OEM) sensors. The P0154 and P0155 codes point specifically to B2S1—the passenger-side first sensor. You’ve replaced the sensor, confirmed heater circuit integrity, but it's still failing. To proceed: check if the sensor voltage readings are stable—either high, low, or open. A scanner is invaluable here because it reveals exactly what the Powertrain Control Module (PCM) is detecting. As a temporary workaround without a scanner, disconnecting the negative battery terminal clears stored heater sensor data from the PCM, allowing it to relearn normal behavior.

I’ve tried replacing the sensor again—both with new and used units—with no change. I’m now noticing inconsistent voltage readings between Bank 1 and Bank 2 sensors. The front sensor (Bank 1) appears to be failing to register a proper heater circuit response, or if it does, the PCM isn’t detecting the signal properly.

I performed the negative battery disconnection procedure as suggested, but the codes returned after driving. The issue persists.

While it's unlikely that multiple sensors are at fault, verify the heater circuit resistance—should be between 3.5 and 14 ohms. A wide range suggests potential wiring or connector issues. However, the most critical step remains using a live data scanner to observe actual sensor voltage behavior (fixed high/low/open). Fuel trim values may also provide clues about how the PCM is adjusting fuel delivery.

I recently replaced the sending unit during winter maintenance, and since then the truck has shown a slightly rough idle. I’m not clear on what 'fuel trims' mean or how to check them. However, when I tested Bank 2 Sensor (B2S1), I got a high voltage reading; when checking Bank 1, the voltage was low.

I suspect the sensor is reporting a fixed low voltage reading—this could explain why the PCM can't interpret it properly.

I’m planning to purchase a new OBD2 scanner with live data capabilities. My current scanner only reads and clears codes—it doesn’t provide real-time sensor or fuel trim values, which are essential for diagnosing this issue accurately.

A reliable scanner is critical—what the PCM is actually 'complaining about' must be seen in real time. Fuel trims (such as STFT and LTFT) indicate whether the engine is adding or subtracting fuel to maintain optimal air-fuel ratio. This data helps pinpoint whether a sensor failure, vacuum leak, or other issue is driving the fault codes.

The PCM is unable to read the B2S1 sensor properly. I’ve double-checked all wiring harness connections—no issues found.

Scanner data: - Fuel System 1: CL (Check Limit) - Fuel System 2: CL - Calculated Load %: 3.1 - STFT B1 %: 0.0 - LTFT B1 %: 5.5 - STFT B2 %: 0.0 - LTFT B2 %: 0.0 - MAP (in hg): 5.6 - Engine RPM: 1566 - MAF (lb/min): 0.9 - TPS %: 15.7

After disconnecting the negative battery, take a good drive to see if the LTFT values adjust over time. Can you view B1S1 O2 sensor voltage readings in real time? This will help confirm whether the sensor is functioning correctly.

The scanner shows data from a freeze frame—no live O2 sensor voltage readings are displayed. I’ll take the truck for a drive and monitor if fuel trim values shift during operation.

Updated readings: - Fuel System 1: OL (Out of Limit) - Fuel System 2: OL - Calculated Load %: 3.5 - STFT B1 %: 0.0 - LTFT B1 %: 7.8 - STFT B2 %: 0.0 - LTFT B2 %: 7.8 - MAP: 10.0 - Engine RPM: 834 - MAF: 1.1 - TPS %: 16.5

Both Bank 1 and Bank 2 are now adding fuel (positive LTFT values), and the MAP reading is low—this suggests a possible vacuum leak or intake system issue. Try the classic 'spray test' using carburetor cleaner to detect leaks at hoses, connectors, or under the hood.

When I replaced the sending unit last winter, the plastic clip securing the vacuum line to the vent solenoid broke. That same day, I noticed a blown 4WS fuse. I plan to relocate the vent solenoid and secure it with a new mounting bracket—though I’m unsure if the original vacuum hose will allow this fix.

I don’t recall a specific TSB for relocating the vent solenoid in 2003 Silverado models. It’s worth checking with your local GM dealer to see if there's an available service kit or technical bulletin addressing this issue.

I performed a vacuum leak spray test under the hood and at the canister and vent solenoid—no leaks detected. I also cleaned the MAP sensor, but that didn’t resolve the issue. After clearing codes, they returned immediately.

Could a cylinder head gasket be failing on the same side as the malfunctioning O2 sensor? I’ve been using engine oil every month to maintain performance—this may indicate underlying combustion or sealing issues.