Preamble: I had kind of hoped to get out of the DIY car maintenance thing as I am rtired and no longer have a garage to work in (its winter) Got the infamous "reduced engine Performance" msg two weeks ago, limped home and got onto the forum to get sped up.

Car seemed to run ok the next day so I drove it to my local volvo guy (not dealer); Just moved here so no relationship/history with mechanics. $750. later the car was running without the msg. They gave me an incomplete list of what they had done (if the list was complete the charges would have been higher...). Cleaned throttle body injector , cleaned and repared cable grounds (TBI and 2 others not identified). Changed oil; nowhere near scheduled but they insisted. They believed the main problem was the cable ground, recommended I get the upstream O2 sensor replaced.



Car ran ok for several days. Instantaneous fuel consumption was very high (35 liters/100km)w hen the car first started rolling.. Three days later it rained fairly hard. Back to Limp mode. Left the car overnite. Cold and dry the next day. Reduced engine performance msg still there but the symptom of max 2000 rpm is not. Drive the car back to garage to have codes read. The following was displayed:

1. Froint heated oxygen sensor bank1 signal too high.

2. Brake pedal sensor – faulty signal

3. Exhaust camshaft control – Slo0wFront heated oxygen sensor signal too lowStop – brake lamp swich outside permitted limits.



I noticed several smal cracks in the flexible (connection between engine and exhaust.



The problem is intermittent for now, possibly related to humidity, so the mechanic wants the car left at the garage so they can see the car fail and debug from thereé



Hoping to avoid (unnecessary expenditures I have these question:

· Is there a way to test the upstream O2 sensor

· Any other simple steps to take before I take the car back to the mecanic?



Please let me know if I should provide more/less detail.

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keep in mind the O2 sensor faults are really telling you what the ECU is seeing as the signal voltage not a direct root cause. "signal too high" is telling you the engine is either running rich and the lambda signal can't correct it enough or you may have an O2 wiring or device issue. Several things can make an engine run rich - MAF, air leak temp sensor, etc so you have to do some additional testing like running an OBD2 real time monitor to see when the engine goes rich (ie when the engine is hot or cold idling or running at speed), you can try inspecting and cleaning the MAF, measure the resistance of the temp sensor, inspect the wires to the O2 sensor and measure the sensor's heater circuit voltage and signal voltage etc. Check youtube for how to vids - I'd bet there's a few out there. Could be the sensor but I wouldn't start by dropping $200 for the part and a roll of the dice :-)