Owners Tips

Goof of the Month: Careful What You Plug into Your OBD Port!

Welcome to Goof of the Month! Every month, we highlight a story or situation that reinforces the need for drivers and shoppers to understand their vehicle, how to maintain it, and how it works.

This month’s story comes to us from Jon Swinden, a dealer service advisor in Sudbury, Ontario. It highlights a simple but important lesson about modern vehicle electronics, and a few good reasons to use care if you plug something into your ride’s on-board diagnostic (OBD) port – including, perhaps, a data recorder provided as a money-saving measure by your insurance company.

The Complaint

Swinden had a customer arrive in a newer crossover that was experiencing numerous issues, which were getting worse. Initially, the customer said her vehicle had been experiencing random warning light illumination, random non-functionality or unintended activation of certain features and functions, and more lately, random bouts of poor engine performance. Then, the customer’s engine started to stall, at random, while she was driving. This prompted her to bring the vehicle in for a look.

“As soon as we see symptoms like this, with lots of warning lights and trouble running smoothly, we plan on an electronics system scan,” Swinden says. “This vehicle had a lot of issues. Literally, every warning light on the instrument cluster was lit up. Sometimes, you see a few warning lights, but in this vehicle, every one of them was on.”

The cause of this wide array of problems was a simple but somewhat surprising one, and Swinden stumbled upon it by accident. When driving the customer’s car into the shop, he noticed a black cable and module near his feet, in the footwell.

“I noticed, right away, that this was plugged into the vehicle’s OBD port, and that the wiring was in pretty bad shape.”

The vehicle’s owner had installed a small module that tracks and monitors driving habits, providing information to her insurance company that could be used to save money on insurance premiums. This device is meant to remain plugged into the OBD port, which all vehicles have beneath their dashboard. The device was connected via a foot-long cable, presumably to facilitate some flexibility to its installation location. Thing is, the customer had simply left the cable, and the module, lying on the floor of the vehicle near the pedals.

Example of frayed wiring Example of frayed wiring (istockphoto.com)

“Over time, after being stepped on and kicked around, the cable that connected this module to the OBD port had become badly worn. The rubber insulation had worn through in several areas, exposing the bare wires inside, which was causing short-circuiting. There was some rust visible too, indicating that the exposed portions of wiring had been in contact with water, probably from wet shoes.”

Though the OBD port uses a fairly small amount of electricity, in theory, the exposed wiring could have caused a fire, or some electrocution. That didn’t happen in this case, but the randomly manifested short circuits were causing a multitude of problems with vehicle systems, all of which were controlled through the vehicle’s ECM, to which this module was attached via the OBD port.

Plug a module into the OBD port, and you’re effectively patching into the vehicle’s engine control module, or ECM, which is the vehicle’s computer brain. The OBD port is a specialized connector with many individual pins and wires connected to that ECM. It’s used for various purposes, including the monitoring and manipulation of a wide range of electronic functions. Plug a frayed, damaged, or shorted-out wiring harness in, and extreme damage to that ECM, and other systems, is likely.

The term “bricked” (which refers to a computer that’s totally ruined), came up in our conversation, several times.

The Outcome

Swinden showed the customer the frayed wiring harness responsible for the numerous problems, explaining that, in simple terms, this was short-circuiting her vehicle’s central nervous system, in real time. The customer said that she’d originally tucked the module out of the way, but that it kept falling down near her feet, so she just gave up and left it on the floor.

Swinden’s technician first unplugged the module and wiring, restarted the car, and confirmed that no warning lights were present. Then, he performed an ECM scan with a diagnostic scanner, which revealed a whopping 14 stored trouble codes, referencing recent electronic problems recorded by the ECM.

OBD-II Scanner Readout OBD-II scanner readout (Nathandm78/YouTube)

“Sometimes, we see 3 or 4 stored trouble codes if a vehicle is really sick. But with 14 codes stored, indicating trouble with all major systems, this could have been a disaster.”

Swinden’s technician cleared the codes, and advised the customer to call him if she saw any more warning lights, which she didn’t.

“This customer got really, really lucky,” Swinden says. “I’m dumbfounded that this didn’t knock her whole ECM, and some other components, out of commission. If it had, she’d have been on the hook for, literally, thousands of dollars.”

Swinden advised the customer that, should she replace the module, she’d need to use some adhesive tape or zip-ties to better secure it in place, in a way that wouldn’t allow the wiring to become damaged.

“I even showed her an estimate to replace and reprogram the ECM on her vehicle, so she’d realize how lucky she got, and install the module properly the next time,” he adds. The estimate for installation of a new ECM was well over $2,000.

Lesson Learned

This customer was lucky: since saving a few bucks a month on car insurance could have cost her thousands of dollars in repairs, parts, and vehicle downtime.

Remember: in much the same way your brain would react unfavourably to having its electrical signals shorted out and mixed up, a vehicle ECU is a sensitive piece of equipment that requires care and caution when things are plugged into it. Properly plugging an approved device into a vehicle OBD port is fine – but if that device, or the cable it’s attached to, is compromised, you’re asking for trouble.

Solution? If you absolutely need to plug something into your OBD port via a cable, be sure the cable is in perfect shape, and secure it in such a way that it won’t be damaged. Follow the instructions carefully, and never modify any of the wiring or pins. And never, ever allow the connection cable to sit in an area where it could be damaged over time – unless you like very expensive repair bills.