The Autel scan tool is a valuable diagnostic device for car owners and mechanics alike. One common trouble code it might display is P1146. This code indicates a problem with the oxygen sensor heater circuit in Bank 1 Sensor 2. This article will delve into the causes of this code, specifically focusing on Nissan vehicles, and outline a potential solution involving a ground sub-harness installation.
Understanding Autel Code P1146
The P1146 code signifies a fault detected in the heater circuit of the downstream oxygen sensor (Sensor 2) located after the catalytic converter on Bank 1 of the engine. The oxygen sensor heater helps the sensor reach operating temperature faster, ensuring accurate readings for proper fuel mixture control and emissions reduction. A malfunctioning heater circuit can lead to inaccurate readings, affecting engine performance and potentially increasing emissions.
P1146 in Nissan Vehicles: A Grounding Issue?
Nissan has identified a potential grounding problem in certain Pathfinder, Frontier, and Xterra models that can trigger various diagnostic trouble codes, including P1146. This issue can often be resolved by installing an additional ground sub-harness. The affected vehicles and associated DTCs include:
- 1996-1997 Pathfinder: P0130, P0150, P0136, P0156
- 1998-2000 Pathfinder: P0131, P0134, P0138, P0140, P0151, P0154, P0158, P0160
- 1999-2001 Frontier (V6): P0131, P0134, P0138, P0140, P0151, P0154, P0158, P0160
- 2000-2001 Xterra (V6): P0131, P0134, P0138, P0140, P0151, P0154, P0158, P0160
- 2002-2004 Frontier (V6): P1143, P0134, P0138, P1163, P0154, P1146, P1166, P0158
- 2002-2004 Xterra (V6): P1143, P0134, P0138, P1163, P0154, P1146, P1166, P0158
Diagnosing and Fixing P1146 with an Autel Scanner
If your Autel scan tool reveals the P1146 code in a Nissan vehicle listed above, follow these steps to diagnose and potentially fix the issue:
1. Voltage Drop Test:
- Use a digital volt-ohm meter (DVOM) to measure the voltage drop between the engine harness ground bolt on the intake manifold and the right-hand (RH) cylinder head.
- With the engine at warm idle, connect the positive (red) lead of the DVOM to the intake manifold ground bolt and the negative (black) lead to the RH cylinder head.
- If the voltage exceeds 0.025V (25 millivolts): This indicates poor grounding. Install the Nissan ground sub-harness as described below.
- If the voltage is below 0.025V (25 millivolts): The issue is not related to grounding and requires further diagnosis using resources like ALLDATA Repair.
2. Installing the Ground Sub-Harness:
- Route the sub-harness along the existing ECCS harness from the RH cylinder head towards the engine’s center front and then back to the intake manifold collector.
- Locate the two threaded holes on the RH cylinder head near the negative battery cable.
- Secure the sub-harness end with the larger eyelets to these holes using the provided hex bolts. Ensure the sub-harness is at least 70mm (2.8 inches) away from the exhaust manifold to prevent heat damage.
- Attach the sub-harness to the ECCS harness at four points using the specified wiring clips, distributing them evenly.
- Secure the remaining sub-harness end with the smaller eyelets to existing ground bolts on the intake manifold.
- Trim any excess material from the wiring clips.
Conclusion
The Autel Scan Tool Code P1146 indicates a problem with the oxygen sensor heater circuit. In specific Nissan models, this can be caused by poor grounding, addressable by installing a ground sub-harness. By following the diagnostic and repair procedures outlined above, you can potentially resolve this issue and ensure proper engine function and emissions control. Always consult official service documentation for detailed instructions and safety precautions before performing any repairs.
