1995 Volvo 850 OBD CODE

First off I am not a Volvo guy, but this is what Volvo says:
Code 4-3-5: Front HO2S Too Slow 1. Check for other codes. If Code 4-3-6 is stored, perform testing for that code first. If Code 4-3-6 is not stored, go to next step. 2. Perform a compression check on all cylinders. Repair as necessary. If compression is okay, go to next step. 3. Check for air leakage in intake system. Repair as necessary. If there is no air leakage in intake system, check for air leakage in exhaust system. Repair as necessary. If there is no air leakage in exhaust system, check fuel and residual pressure. Repair as necessary. If fuel and residual pressure are okay, retest using new front HO2S. Code 4-3-6: Rear HO2S Compensation 1. Check for other codes. If Code 4-2-5 is stored, perform testing for that code first. If Code4-2-5 is not stored, go to next step. 2. Perform a compression check on all cylinders. Repair as necessary. If compression is okay, go to next step. 3. Check for air leakage in intake system. Repair as necessary. If there is no air leakage in intake system, check for air leakage in exhaust system. Repair as necessary. If there is no air leakage in exhaust system, check fuel and residual pressure. Repair as necessary. If fuel and residual pressure are okay, go to next step. 4. Turn ignition on. Connect fuel pressure gauge to system. Squeeze hose between EVAP valve and intake manifold with Hose Pliers (115 8957). Code for EVAP system can be set. Start engine and run at idle until rear HO2S starts operating. Rear HO2S starts operating a short time after rear HO2S preheating starts. 5. Increase fuel pressure by squeezing hose after fuel pressure regulator with Hose Pliers (115 8957). Voltage across rear HO2S terminals should increase to about.8 volt. Remove hose pliers. Remove instrument cluster hose at intake manifold. If voltage across rear HO2S terminals drops to about zero volts, retest using new front HO2S. If voltage across rear HO2S terminals does not drop to about zero volts, retest using new rear HO2S.