Limp-home mode
I’ve owned my Volvo S60 with the D5244T engine for eight years and it has done 142,000 miles. The engine generally runs well with no smoke and the emissions are fine. Five years ago, it had an intermittent fault which is now getting worse: when going up long hills or accelerating from low revs (high vacuum), the engine service light come on. The engine then goes into ‘limp-home’ mode, with no power from the turbo until the revs reach about 2000rpm, when it kicks in with full power. If you turn off the ignition and restart, all is well until the next time.
I can predict when it’s going to happen, but there are no obvious signs, although it happens more often with passengers in the car. I had the fault codes read a few years ago, which I think indicated air leaks. However, as far as I can tell, the original rubber hoses and clips are all OK, including to the intercooler.
I understand it could be the TPS and MAF sensors sending conflicting messages to the ECU. I once cleaned the MAF sensor with carb cleaner and it seemed to improve matters, but recently it has been getting worse and cleaning the sensor has not made any difference. It has been suggested it could be a sticking EGR valve, so could you suggest a cleaner which may help?
Peter Sunderland
You have not mentioned the year of your Volvo, but as it has the D5244T engine I am assuming it was made between 2001 and 2006, unless you have missed off the last digit of the engine number (either a 2, 3 or 4). An accurate diagnosis would mean reading the fault codes from the car’s ECU. These may vary from the code you received several years ago, and may in fact be unrelated, but they should point directly to the cause of the light illuminating. As turning the ignition off and on again resets the light, this does indicate an engine management problem. This could be due to one of many reasons, but as you mention that cleaning the MAF sensor used to make a positive difference, I suspect the sensor may no longer be serviceable. The hot-wire sensor inside the MAF does not have an indefinite lifespan and will eventually reach a stage where cleaning it will no longer restore its operation.
Another likely candidate is the turbocharger boost pressure sensor. This may be recording an overboost, which would put the engine into ‘limp-home’ mode. Turning off the ignition will reset the system, but the problem will return when the sensor again records too high a boost pressure.
The system may also be recording a high boost pressure due to either a faulty turbo solenoid, actuator or sticking variable vanes in the turbo – all of these are common issues. By physically moving the actuator rod you may be able to detect if the fault is with the variable vanes sticking. The use of a vacuum pump would help detect if the fault was in the actuator and would also detect any leaks in the vacuum system.
As the fault has been present for quite a while, and as you have checked the intercooler and hoses, I would not suspect these as being the cause of problem – a faulty intercooler hose would have failed completely by now.
Finally, it may be the EGR valve at fault. This could be sticking, so using an appropriate cleaner such as Wynn’s Diesel EGR Extreme Cleaner may help with any carbon issues in both the EGR valve and turbo.