It’s a common question among car owners: can I start my car while an OBD2 scanner is plugged in? The short answer is generally yes, you can start your car with an OBD2 scanner connected. However, there are specific situations where having an OBD2 scanner plugged in might actually be related to starting problems, although not in the way you might initially think. This article will explore this potential issue and guide you on what to check if you suspect your OBD2 scanner is interfering with your car’s starting process.
In some instances, an OBD2 scanner being plugged in can mask or even contribute to an underlying electrical problem, specifically related to vehicle grounding. A user on a Honda Civic forum encountered a perplexing situation where their car exhibited inconsistent spark across all cylinders after an engine reassembly. Interestingly, they discovered a link between their OBD2 scanner and the engine’s ability to function.
The key insight from this forum discussion was that when the OBD2 scanner was plugged in, it inadvertently provided a ground to the Engine Control Unit (ECU) or Powertrain Control Module (PCM) through one of its pins. When the scanner was removed, this supplemental ground was lost.
This scenario highlights that if your vehicle has a weak or faulty ground connection, plugging in an OBD2 scanner might temporarily bridge that gap, allowing the ECU to function correctly and potentially enabling the car to start. However, this is not a solution, but rather a symptom indicator. When the scanner is unplugged, the original grounding issue resurfaces, potentially preventing the ECU from consistently providing spark to the cylinders. Without proper grounding, the ECU might struggle to operate correctly, leading to symptoms like:
- Inconsistent or weak spark: The engine might crank, but fail to start or run erratically.
- Engine flooding: Unignited fuel can accumulate in the cylinders because of the lack of consistent spark.
- Starting issues only when OBD2 scanner is unplugged: This is the crucial symptom pointing towards a potential grounding problem masked by the scanner.
If you suspect a grounding issue, especially if you notice your car starts fine with the OBD2 scanner plugged in but struggles or fails to start when it’s removed, it’s crucial to check your vehicle’s ground connections. A multimeter is an essential tool for this diagnosis.
How to test car ground with a multimeter
As demonstrated in the video “How To Use a Multimeter – Test Car’s Ground – Video 3 – YouTube“, you can effectively test the strength of a ground connection. The process involves setting your multimeter to measure resistance (Ohms Ω) and placing one probe on the negative battery terminal and the other on the ground point you want to test. A good ground connection will exhibit very low resistance, ideally close to 0 Ohms. High resistance indicates a weak or faulty ground.
To rectify a weak ground, locate the grounding points in your engine bay and chassis. These are typically points where ground wires are bolted to the metal body or engine block. Once identified, follow these steps:
- Disconnect the Battery: Always prioritize safety by disconnecting the negative battery terminal before working on any electrical components.
- Clean Grounding Points: Use a wire brush (brass or steel) and electrical contact cleaner or parts cleaner to thoroughly clean the metal-to-metal contact surfaces. Remove any corrosion, rust, paint, or grime that could impede electrical conductivity.
- Secure Connections: Ensure that all bolts and nuts securing the ground wires are tightened adequately to provide a firm and reliable electrical connection.
By meticulously cleaning and tightening your vehicle’s ground connections, you can eliminate potential grounding issues that might be causing starting problems and ensure the ECU and other electrical components function correctly, regardless of whether an OBD2 scanner is plugged in. Remember, the OBD2 scanner highlighting this issue is a symptom pointer, and addressing the root cause – the weak ground – is the key to resolving the problem.
