How I Restored Performance on a 2003 Jaguar S Type R
Recently, a Jaguar S Type R was brought in with a coolant leak. I fixed the leak, but the “Restricted Performance” warning on the dashboard persisted. The owner and I initially thought that the warning was due to the low coolant, but it was still present even after fixing the leak.
To diagnose the issue, I connected the car’s computer to my Altel scanner and found a few codes. After clearing them, I noticed a heater circuit code on one of the O2 sensors. Although the computer was reporting substituted values for the Air Fuel ratio because of the set code, testing the resistance of the heater circuit confirmed that the sensor was bad. After replacing it, the car ran better, but the “Restricted Performance” warning was still present.
I then discovered an intermittent knock sensor fault as the only remaining code. However, I wasn’t excited about removing the intake manifold to replace the sensors, so I decided to test them first. I located the connectors at the front of the engine and used an oscilloscope to monitor their output while tapping the engine with a hammer. The trace was positive, indicating that the sensors were good.
Upon closer inspection, I realized that one of the connectors was in the area where the coolant leak had occurred. I cleaned the connectors and sprayed some Deoxit on them. Remarkably, both the knock sensor code and the “Restricted Performance” warning disappeared!
In conclusion, sometimes the simplest solution can be the most effective one. It’s always worth checking the connectors and using diagnostic tools to solve car problems. Don’t give up until you find the root cause of the issue.