Reductant Injector Circ Low Bank2 Unit 1


The PCM has detected a malfunction in the reductant injector air pressure sensor circuit. The reductant injector is used to reduce noxious gases being expelled via the diesel particulate filter (diesel engines) or catalytic converter (gasoline fueled engines, especially turbocharged). Bank 2 indicates the bank of the engine which contains the number two cylinder. See the manufacturer’s service manual (or equivalent) for the location of the number two cylinder. Unit 1 denotes the pre diesel particulate filter or catalytic converter (or upstream) sensor.

Code Set Parameters

The reductant injector air pressure sensor utilizes sensors in the exhaust system to input voltage readings to the PCM. These voltage readings are typically recognized by the PCM as exhaust gas temperature or pressure (depending upon manufacturer and model). Variations in system voltage that exceed manufacturer’s predetermined limitations will cause a code to be stored and possibly a service engine soon lamp to be illuminated. Some models require multiple drive cycles in order for a service engine soon lamp to be illuminated.


Other than excessive black smoke upon acceleration, there will probably be no obvious codes other than an illuminated service engine soon lamp and possibly a stored trouble code.

Common Causes

Loose, broken, burned, or corroded wiring and/or terminals and connectors are the most common cause of this trouble code bring stored. Other causes may include the exhaust gas temperature sensor being shorted internally (or to ground), a faulty sensor, the presence of an aftermarket off road exhaust system that causes a decrease in back pressure, a severe exhaust leak upstream from the exhaust temperature sensor will also cause this code to be stored.

Common Misdiagnosis

The most common source of mishaps when diagnosing this code comes from mistaken identity. Frequently the oxygen sensor is either mistaken for the exhaust gas temperature sensor or it is believed that the exhaust gas temp sensor is integrated into the heated oxygen sensor. Of course, this is incorrect and replacement of the oxygen sensor/s will not lead to a successful diagnosis.


  • Reductant injection systems are used in all types of vehicle exhaust systems but are used much more often in diesel applications. Reductant injection systems use either water, a chemical agent, air, or a combination of the three to reduce exhaust emissions in automotive applications by reducing exhaust temperature and/or exhaust pressure in the diesel particulate filter or catalytic converter assembly
  • The reductant injector is mounted directly on the diesel particulate filter or catalytic converter and it is normally controlled electronically using a dedicated reductant injector controller that is used in conjunction with the PCM
  • If the PCM detects an abnormally high exhaust temperature, pressure, and/or noxious gas concentration, the reductant injector is activated and the reductant compound is sprayed into the diesel particulate filter or catalytic converter
  • The reductant compound in turn helps to reduce the exhaust gas temperature and/or pressure and noxious gases. The exhaust gas temperature sensor is typically a 2-wire sensor located in the exhaust down pipe
  • The exhaust gas temperature sensor is used in diesel engines, gasoline burning engines, and even turbocharged engines
  • In diesel engines, the sensor will likely be located near the diesel particulate filter section of the exhaust system
  • Turbocharged applications may place the exhaust gas temperature sensor in the exhaust input pipe, near the turbocharger
  • The exhaust gas temperature sensor is of the temperature reactive resistor variety
  • The sensor is supplied with a low voltage (usually 5-volts) power wire and a ground wire
  • As exhaust gas temperature increases, the level of resistance in the sensor decreases, allowing the feedback voltage signal to the PCM to increase
  • As exhaust temperature decreases (with the engine off), circuit resistance increases and the feedback voltage signal to the PCM decreases
  • The PCM recognizes these voltage variations as exhaust gas temperature and it reacts accordingly, adjusting ignition timing or the air/fuel ratio in order to lower the exhaust gas temperature and protect the catalytic converter. When the PCM demands the reductant injector “ON” it begins to monitor the upstream and downstream exhaust gas temperature, exhaust gas pressure, or heated oxygen sensor/s to determine if there is sufficient reduction temperature, pressure, or noxious gas levels
  • If the downstream levels fail to display significant reduction, a code will be stored and a service engine soon lamp may be illuminated
  • Several tools will be instrumental in successfully diagnosing this code
  • A suitable OBD-II scanner (or code reader) and a digital volt/ohmmeter will be most helpful in performing a successful diagnosis
  • An infrared thermometer with a laser pointer will also be helpful
  • Begin with a visual inspection of all wiring and connectors
  • Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary
  • Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data
  • This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored
  • Continue by clearing the code and operating the vehicle to see if it returns
  • This will help to determine whether or not the malfunction is intermittent
  • After the codes are cleared, test drive the vehicle to see if the code returns
  • If the code fails to immediately return, you may have an intermittent condition
  • Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made
  • Continue your diagnosis with a visual inspection of the exhaust gas temperature/pressure (or heated oxygen) sensors and system circuitry
  • Pay close attention to areas where wiring and connectors are located near hot exhaust components
  • If all of the exhaust gas temperature/pressure (or heated oxygen) sensor circuitry appears to be in proper working order, then proceed with the diagnostic procedure
  • If certain items appear to be damaged, burned, or corroded, repair or replace them as required, then reset the code and retest the system. If no burned, damaged, or shorted wiring or loose connectors are detected, disconnect the exhaust gas temperature/pressure (or heated oxygen) sensor connector and remove the exhaust gas temperature sensor
  • Using the digital volt/ohmmeter, check the resistance of the exhaust gas temp/pressure (or heated oxygen) sensor
  • Typical resistance for this sensor should be approximately 150 ohms but double check manufacturer’s specifications prior to testing
  • Normally, if there is less than 50 ohms of resistance, then you would replace the sensor
  • If the initial resistance is within specifications, leave the leads of the digital volt/ohmmeter connected and heat the resistor with a heat gun
  • Carefully observe the resistance level of the sensor (on the screen of the digital volt/ohmmeter) as the temperature is elevated to see if it decreases smoothly
  • If the resistance level does not decrease with heat and increase as it cools, replace the sensor. If everything has checked out thus far, turn the key to the “ON” position and test for the presence of a voltage (and a ground signal) at the exhaust gas temperature/pressure (or heated oxygen) sensor electrical connector
  • If there is no low voltage (usually 5-volts) on the signal wire, disconnect the PCM connector and perform a continuity test on the wire using the digital volt/ohmmeter
  • If there is continuity, the PCM may be faulty (PCM failure is rare and, if replaced, it will need to be reprogrammed)
  • If no ground is present locate the source and check for continuity using the digital volt/ohmmeter
  • Repair or replace open or shorted wiring and connectors as required. If there is no voltage present on the sensor connector and all system circuitry is functioning normally, suspect a faulty reductant injector air controller
  • Controller failure is rare and will likely require reprogramming. Installing high performance exhaust systems (with no catalytic converters) can also cause this code to be set due to the lack of exhaust system back pressure
  • This condition can be rectified by installing an in line resistor (2.5 ohms) between the signal and ground wires and leaving the exhaust gas temperature sensor disconnected
  • The PCM will read the sensor resistance and pass it
  • Check local, state, and federal laws before removing emission related components