Palmer's Auto Care Podcast

Palmer's Auto Care Podcast


Solving the Mystery of the Check Engine Warning Light PAC002

April 09, 2019

Palmer's Auto Care Podcast by Neil Palmer Jr. & Dave Eastman
In this episode Neil and Dave discuss the mysterious check engine warning light that can come on without notice, and stay on for no apparent reason. The vehicle driver may be responsible for the light if the engines oil or coolant are low, if maintenance has been neglected, or if the gas cap is loose. The light can also come on even if the vehicle has been properly maintained. A failed sensors or loose wire connection can cause the dash light to illuminate.

This warning light is the most common symbol to light up on a cars dash. There is a lot of confusion about what the light means. The light can turn on and off depending on the problem. It could come on under different conditions such as: at certain temperatures; after the car has been running a specific time; over bumps; at specific engine or vehicle speed, or due to a number of other conditions.

Every week Neil gets several calls or customer complaints like “my car is running ok but the check engine light is on” or “my car running poorly and light is on”.

When the light is on a computer has recognized a problem and turned the light on. It may be a temporary problem that will go away and the light will go out, or it may stay on.

When a code is read, it is just a description of the symptoms of the failure and is only to lead a mechanic in the direction to find the problem. Only around 60% of the time is the code pointing to the exact problem.

It’s important to not just read the code and if it relates to a sensor, to replace the sensor. That can be a waste of money if the sensor is not bad. The sensor may be affected by some other problem – extra air due to a vacuum leak, some other sensor sending a wrong signal, or a mechanical problem.

When the light is on the vehicles exhaust emission are higher than normal. The vehicle fuel economy may be affected. Also the problem should be addressed soon because it can cause harm to the vehicle.
Reprogramming computers fixes many car problems
Neil also pointed out that some fixes do not require part replacement to be repaired. He mentioned a GMC Envoy with a window problem that had no bad parts. It had a computer software problem that required reprogramming to fix the problem. If a shop or car owner tried to repair it with parts replacements, they would never get it fixed.

Neil described a classic scenario he sees in Palmer’s Automotive frequently. A vehicle with codes P0171 and P0174, which indicate bank 1 and bank 2 are lean. The computer data says it is an Oxygen sensor code. If a customer has the code read and decides to buy oxygen sensors it won’t fix the problem. The vehicle has a fuel delivery problem, a vacuum leak, an air temp sensor problem, or a mass airflow sensor problem.

Another situation that happens almost weekly at Palmer’s Automotive is when a customer has a code read at the parts house and calls or comes by the shop to have the sensor, the code relates to, replaced. If Neil replaced the sensor as requested and it didn’t fix the dash warning light, the customer would be upset. That is the reason Neil never replaces a part without first performing proper diagnostics. He wants his customer to be happy with his service and he knows many wouldn’t be if he didn’t follow proper diagnostic procedures.

Dave asked Neil to talked about his training and the equipment required when performing automotive diagnostics on engine electronics and other computer controlled systems. Neil said he and his staff go to six vehicle specific training courses every year. He said the equipment required to diagnose these systems runs more than $10,000.

Neil made one last point about diagnosing electronic problems. If you have a car with a problem don’t call a shop and ask what it cost to fix it.