Technical Description of OBD-II Trouble Code
The circuit for the Catalyst Temperature Sensor is registering a low reading (Bank 1, Sensor 2).
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 (Subaru, Ford, Chevy, Jeep, Nissan, Mercedes-Benz, Toyota, Dodge, etc.). While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
The catalytic converter is a crucial component of a vehicle’s emissions equipment. It facilitates a chemical reaction in which exhaust gases are converted into harmless water (H2O) and carbon dioxide (CO2). This reaction involves the conversion of carbon monoxide (CO), hydrocarbon (HO), and nitrogen oxides (NOx).
The efficiency of the catalytic 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 (O2), the powertrain control module (PCM) can determine if the catalytic converter is functioning correctly. 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 properly, the downstream sensor should maintain a steady reading of around 0.45 volts.
The efficiency and temperature of the catalytic converter are closely related. If the converter is functioning correctly, the outlet temperature should be slightly higher than the inlet temperature. In the past, a temperature difference of 100 degrees Fahrenheit was considered normal. However, modern vehicles may not exhibit such a significant difference.
It is important to note that 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 2” refers to the sensor located downstream of the catalytic converter.
Trouble code P042C is triggered when the PCM detects a low signal from the catalyst temperature sensor in the bank 1, catalyst temperature sensor 2 circuit. This usually indicates a short circuit.
Code Severity & Symptoms
This code has a moderate severity level. Symptoms of a P042C engine code may include:
Causes
Possible causes for this P042C code include:
Diagnostic and Repair Procedures
Begin by visually inspecting the downstream oxygen sensor and its corresponding wiring. Look for loose connections, damaged wiring, etc. Additionally, check for any exhaust leaks visually and audibly. An exhaust leak can trigger a false oxygen sensor code. If any damage is found, repair it as necessary, clear the code, and monitor if it reappears.
Next, check for any technical service bulletins (TSBs) related to this issue. If no relevant information is found, proceed with a step-by-step diagnosis of the system. The following is a general procedure, as the testing process for this code can vary between vehicles. For accurate testing, refer to a diagnostic flow chart specific to the make and model of your vehicle.
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, ideally, an oscilloscope. Since most individuals do not have access to a scope, we will cover oxygen sensor diagnosis using a scan tool. Connect the scan tool to the ODB port under the dash. Turn on the scan tool and select the Bank 1 Sensor 2 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 maintain a steady reading of 0.45 volts with only minimal fluctuations. If it is not responding correctly, it will likely need to be replaced.
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 displays 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 displays a numeric value, there is continuity to ground.
Finally, check that the PCM is processing the O2 sensor signal correctly. 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.
