Introduction
As cars have gotten more technologically advanced over the years, they have become increasingly reliant on complex electrical systems and computer modules to control everything from the engine and transmission to safety features like airbags and anti-lock brakes. This technology brings many benefits, but it also means there is more that can go wrong electrically in a modern car. When you experience strange electrical gremlins or have a faulty computer module, it can be infuriating trying to get to the bottom of the issue. However, with some basic diagnostic steps and troubleshooting techniques, I can systematically track down the source of the problem and get your car back to running properly again.
Understanding On-Board Diagnostics (OBD)
The first tool I utilize when troubleshooting electrical issues in a car is the on-board diagnostics (OBD) system. OBD is the computer system built into all cars manufactured since 1996 that monitors the performance of the engine, transmission, airbags, antilock brakes, and other systems. It stores diagnostic trouble codes (DTCs) when it detects issues, which gives me a starting point for diagnosing problems. I connect an OBD2 scanner tool to access the car's computer and read any stored DTCs that may point me in the direction of the faulty module or wiring.
For example, a P0650 DTC indicates an issue with the malfunction indicator lamp (MIL) control circuit, while a U0101 DTC suggests a lost communication with the transmission control module (TCM). OBD trouble codes don't always pinpoint the exact problem, but they give me a general area to focus my diagnostic work. I use the codes in conjunction with a thorough physical inspection and testing of components.
Inspecting Wiring and Connections
Electrical gremlins are often caused by damaged wiring or bad connections rather than failed components. Once I check for trouble codes, I thoroughly inspect the wiring harnesses and electrical connectors around any modules or sensors that were flagged. I look for:
- Frayed, cut, or rubbed through wiring insulation
- Corroded or burnt terminals and pins
- Loose, damaged, or missing connectors
- Signs of moisture or liquid damage
If I find any suspect wiring or connectors, I repair or replace them and then clear the OBD trouble codes to see if the issue has been resolved before moving on to more complex diagnostics.
Testing with a Multimeter
After inspecting the wiring, my next step is verifying the integrity of electrical circuits with a multimeter. I backprobe connectors to test for power and ground at different points in suspect circuits indicated by trouble codes or symptoms.
For example, if the engine cranks but won't start, I may test:
- Power and ground at the crankshaft position sensor - if no power, the circuit has a wiring issue
- Crankshaft sensor resistance - if out of spec, the sensor is faulty
- 5V reference voltage at the camshaft sensor - if no/low voltage, the PCM power supply could be bad
Methodically testing circuits gives me a clear picture of where power is missing in the circuit. I use the service manual wiring diagrams to follow the flow and isolate the failure.
Checking for ECM/PCM Firmware Updates
Some electrical issues are caused not by hardware failures but by bugs in the programming of the electronic control module (ECM) or powertrain control module (PCM). Many automakers issue updated firmware to fix bugs and improve performance. Before condemning a module as faulty, I always check for the latest firmware updates from the automaker and reflash the ECM/PCM if an update is available. This simple update can save the time and expense of replacing an ECM/PCM unnecessarily.
Swapping or Replacing Modules
If I've narrowed down the issue to a specific module based on trouble codes, wiring tests, and process of elimination, replacing the faulty control module is often the solution. For newer cars where modules are expensive, I sometimes swap in a known-good used module from a salvage yard as a test before buying a new module. If the symptoms go away, I can confirm the original module was the issue.
Replacing modules requires recalibrating the replacement to the car using factory scan tools. I take care to buy the correct part number module for the specific vehicle and model year. Installing the wrong part is asking for problems. With the proper module installed and coded correctly, most electrical gremlins and faults will disappear.
Seeking Help at the Dealership
In rare cases, after extensive troubleshooting and testing I still can't resolve an electrical issue. Newer cars are so complex that specialized factory tools and software are sometimes needed, especially for problems in hybrid/electric vehicles and advanced driver assist systems. When I hit a dead end, I rely on the dealership service technicians with access to factory tools, software, and information directly from the automaker. The solution may be reprogramming modules, installing a software update, or even replacing firmware in the vehicle's various computers.
Patience and Diligence Are Key
It can be frustrating chasing down electrical gremlins, but methodical diagnostic steps allow me to zero in on the source in the vast maze of wires, connections, modules and computers in a modern vehicle. While it requires patience and diligence, taking the time to troubleshoot avoids throwing parts at a problem or accidentally making the situation worse. When done properly, I can resolve the most elusive electrical faults and get the car running right again without the headaches.