BY Neil Currie In this month’s article I decided to write about a recent vehicle I had in the workshop which turned out to be rather interesting when the cause was found. The fault was man-made, and these can be the trickiest to solve, especially when it is an electrical fault. This is because software engineers do not write software to anticipate someone manipulating circuits or changing it from how it was originally designed. The vehicle in question was a Toyota Pro Ace van, more commonly recognised as a Peugeot Expert, the only difference being Toyota badges. The van was originally brought in with a blown turbocharger which had failed mechanically. Once this was replaced by my colleague, the van was road tested. However, it had no boost and quickly went into limp home mode storing an under boost code. Returning to the workshop, it was checked over and it was found that there was no vacuum to the turbo actuator. A few checks were done to make sure everything was where it should be, which they were and at this point the vehicle was handed over to me to have a look. The 2.0 diesel engine fitted to this van uses a vacuum controlled waste gate actuator. The actuator itself also has a position sensor fitted, and starting the vehicle showed the engine control module command to demand a position of 90%. Despite this, the actual position stayed at 0% confirming the complaint. I decided to first test at the control solenoid which was placed awkwardly down the back of the engine, unbolting the solenoid and gaining access to the pipework allowed me to carry out some checks, on this solenoid we have 3 pipes, the first a vacuum supply in, the second which is the vacuum output which goes to the turbo to control the waste gate and the third to atmosphere to allow the solenoid to release excess vacuum when required, as with the solenoid being constantly supplied vacuum it cannot release vacuum via 30 AFTERMARKET APRIL 2024 TECHNICAL www.aftermarketonline.net FACE THE PRO ACE Neil finds that the most dangerous game is indeed man, when a mistake made by a mechanic in the past proves to be a real head-scratcher the turbo actuator as this would cause the turbo actuator to over boost which is not what we want. For my first check I applied vacuum to the outlet pipe to the turbo watching live data on the scan tool to make sure the pipe was ok and the turbo actuator was capable of moving. This test showed the position to move to 90% like the command from the engine ECU was asking for so my problem lay elsewhere. Next, I started the engine and checked vacuum supply to the solenoid. My gauge showed a healthy vacuum of 30inHg (inches of mercury) and testing the last pipe showed a clear route to atmosphere. This meant my problem lay either in the solenoid itself or the control from the ECU. The solenoid is controlled using Pulse Width Modulation (PWM). Please refer to Fig.1. This is where on this particular component, the ECU sends a 12v supply to one side of the solenoid and as the solenoid is a effectively a coil of wire, the voltage flows through it and back down the other wire to the control unit. When it wants the solenoid to operate, it quickly pulses the return wire to ground over and over continuously while maintaining battery voltage on the supply side, this voltage difference causes the solenoid to work and it does this at such a rate of change that it can accurately control the speed and movement of the solenoid which we refer to as the duty cycle. By doing this the solenoid can be operated at any position from 0 to effectively 100% allowing much finer control compared to how it was previously done by feeding a power and ground to a component and it was either on or off, also by using PWM the current consumption of the component is much lower so lighter wiring can be using saving on production costs. Testing the solenoid Upon testing the solenoid for control it was noted there was 12v on both wires as expected. If we only had one 12v Fig. 1
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