In past podcasts, we’ve looked at specific DTCs and have broken down what techs should look for when diagnosing a vehicle with that code.
Today, we’re taking a slightly different approach and discussing a specific vehicle that was brought into the shop of one of TechShop’s contributors, Olle Gladso. A customer of Olle’s brought in a 2003 Mitsubishi Eclipse with the 4G64 2.4 liter and a complaint of a rough running condition and a no-start when warm. A DTC scan revealed DTC P0340, or CMP (camshaft position sensor) Circuit Malfunction Bank 1.
At first look, the repair appeared uncomplicated. When the engine was cold, it started right up and ran smoothly. However, if the engine was warm, it would not restart once it was shut off.
When Olle connected his oscilloscope, the waveform showed that when the output voltage should have been close to zero volts, it was far from it. As the working temperature of the engine increased, the low point of the waveform became 4 volts. The PCM didn’t recognize this as a valid signal so it didn’t open the injectors. Since this type of failure is common, they stopped testing and installed a new CMP.