CARS OnDemand video: No code diagnosis

by | Oct 24, 2019 | 0 comments

CARS OnDemand instructor Will Carcone offers this video tip for automotive professionals on No Code Diagnosis that can cause no-start conditions, particularly in cold conditions, and other problems but can be difficult to diagnose.

By Will Carcone, CARS OnDemand Instructor

A common concern we receive at the CARS Technician Assistance Centre regards vehicles with a No-Code Fault condition.

Isolating the source of a no-code condition is becoming increasingly difficult. The types of conditions I am talking about are no start, hard-starting and cut-out or stalling problems that don’t set diagnostic test codes.

These issues are common but sometimes difficult challenges for technicians. In the CARS OnDemand course, No-Code Diagnosis, we demonstrate effective methods to diagnose and repair these situations.

One important aspect is knowing sensor relationships, to determine if one is reading incorrectly.

Now in this example, we see both the coolant temp sensor and the intake air temp sensor.

When a vehicle is cold and has not been started, the intake air temperature sensor should measure close to ambient temperature. The coolant temp sensor should be within 10 percent of the intake air temp sensor reading. Of course, that percentage will change if the vehicle is started or has been running.

In our example, the coolant temperature sensor shows 61 degrees Celsius, while the ambient air temperature sensor shows 45 degrees Celsius. As it is not within 10 per cent, the discrepancy indicates that the vehicle in fact has been or is running.

Noting this sensor error is important when we have a no-start condition due to over-fuelling or flooding on cold starts. Many PCMs will use the coolant sensor data to determine the amount of fuel needed for start-up.

The course highlights many different sensors and their operation in today’s modern vehicles, which is important to know in order to repair no-code fault situations.

The full CARS OnDemand No Code Diagnosis course, along with hundreds of other automotive-related lessons, is available to CARS OnDemand participants at


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