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Technical Description of OBD-II Trouble Code
The circuit for the Catalyst Temperature Sensor is registering a high reading on Bank 1, Sensor 1.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to OBD-II equipped vehicles with a catalyst temperature sensor. This includes vehicles from Subaru, Ford, Chevy, Jeep, Nissan, Mercedes-Benz, Toyota, Dodge, and others. While the code is generic, the specific repair steps may vary depending on the make and model of the vehicle.
The catalytic converter plays a crucial role in reducing emissions in a vehicle. Exhaust gases pass through the catalytic converter, where a chemical reaction occurs. This reaction converts carbon monoxide (CO), hydrocarbon (HO), and nitrogen oxides (NOx) into harmless water (H2O) and carbon dioxide (CO2).
The efficiency of the converter is monitored by two oxygen sensors: one located upstream from the converter and one located downstream. By comparing the signals from these oxygen sensors, the powertrain control module (PCM) can determine if the catalytic converter is functioning properly. A standard zirconium prealyst O2 sensor will rapidly switch its output signal between approximately 0.1 and 0.9 volts. A reading of 0.1 volts indicates a lean air/fuel mixture, while 0.9 volts indicates a rich mixture. If the converter is operating correctly, the downstream sensor should consistently read around 0.45 volts.
The efficiency and temperature of the catalytic converter are closely related. If the converter is functioning properly, the outlet temperature should be slightly higher than the inlet temperature. In the past, a temperature difference of 100 degrees Fahrenheit was considered normal, but modern vehicles may not exhibit such a significant difference.
There is no actual “catalyst temperature sensor.” The codes mentioned in this article are referring to the oxygen sensor. The “bank 1” portion of the code indicates that the issue is with the first bank of the engine, which includes cylinder #1. “Sensor 1” refers to the sensor located upstream of the catalytic converter.
Trouble code P0428 is triggered when the PCM detects a signal from the catalyst temperature sensor, usually indicating an open circuit.
Other related diagnostic codes include:
Code Severity & Symptoms
This code has a moderate severity level. Symptoms of a P0428 engine code may include:
Causes
Possible causes for this P0428 code include:
Diagnostic and Repair Procedures
Begin by visually inspecting the upstream oxygen sensor and its wiring. Look for loose connections, damaged wiring, or any other issues. Also, check for exhaust leaks visually and audibly, as an exhaust leak can trigger a false oxygen sensor code. If any damage is found, repair it as necessary, clear the code, and see if it reappears.
Next, check for any technical service bulletins (TSBs) related to this issue. If no relevant TSBs are found, you will need to proceed with step-by-step diagnosis of the system. The following procedure is a general guideline, as testing for this code can vary between vehicles. For accurate testing, refer to a diagnostic flow chart specific to your vehicle’s make and model.
Check for other DTCs
Oxygen sensor codes are often triggered by engine performance problems that result in an imbalanced air/fuel mixture. If there are any other DTCs stored, address those first before proceeding with oxygen sensor diagnosis.
Check Sensor Operation
The best way to do this is by using a scan tool or an oscilloscope. Since most individuals don’t have access to an oscilloscope, we will cover oxygen sensor diagnosis using a scan tool. Connect the scan tool to the OBD port under the dash, turn it on, and select the Bank 2 Sensor 1 voltage parameter from the data list. Bring the engine up to operating temperature and observe the sensor’s operation on the scan tool in graph mode. The sensor should rapidly switch between rich and lean (0.1 volts and 0.9 volts). If the sensor’s response is sluggish, it is likely faulty and should be replaced.
If the sensor consistently reads above 0.55 volts, it could indicate a failed sensor, a too-rich air/fuel mixture, or an open in the sensor signal circuit. If the sensor consistently reads above 0.35 volts, it could indicate a failed sensor, a too-lean air/fuel mixture, or high resistance or a short in the signal wire to the PCM.
Check the circuit
Oxygen sensors generate their own voltage signal, which is sent back to the PCM. Before proceeding, consult the factory wiring diagrams to determine the function of each wire. Autozone offers free online repair manuals for many vehicles, and ALLDATADIY offers single vehicle subscriptions. To check for continuity between the sensor and PCM, turn the ignition key to the “off” position and disconnect the O2 sensor connector. Connect a digital multimeter set to ohms (with the ignition off) between the O2 sensor signal terminal on the PCM and the signal wire. If the meter reads “out of limits” (OL), there is an open circuit between the PCM and sensor that needs to be located and repaired. If the meter reads a numeric value, there is continuity.
Next, check the ground side of the circuit. Turn the ignition key to the “off” position and disconnect the O2 sensor connector. Connect a digital multimeter set to ohms (with the ignition off) between the O2 sensor connector ground terminal (harness side) and chassis ground. If the meter reads “out of limits” (OL), there is an open circuit on the ground side that needs to be located and repaired. If the meter reads a numeric value, there is continuity to ground.
Finally, check that the PCM is processing the O2 sensor signal properly. Leave all the connectors attached and insert a back-probe meter lead into the signal terminal at the PCM. Set the digital multimeter to the DC volts setting. With the engine warmed up, compare the voltage reading on the meter to that on the scan tool. If the two readings do not match, the PCM is likely faulty or requires reprogramming.
Professional Service
While we always recommend seeking professional mechanical assistance to resolve this issue, if that is not possible, we offer the option to permanently delete this specific DTC. All other codes will continue to function normally. If you are interested in this option, please upload your ECU file to our portal.
