anengineer Posted March 15, 2004 Report Share Posted March 15, 2004 I've recently begun consistantly getting codes PO17 and PO42. Looking at PCM data I'm seeing: PD30 - 3.7 PD31 - 3.7 PD32 - .00 (at idle) ; 0 (rev'd to 2000rpm) PD33 - .86 " ; .05 thru .86 (rev'd to 2000rpm) PD34 - 0 " ; 0 (rev'd to 2000rpm) PD35 - 0 " ; 0 thru 5 (rev'd to 2000rpm) PD36 - 180 " ; 180 thru 170 (rev'd to 2000rpm) PD37 - 127 " ; 127 thru 132 (rev'd to 2000rpm) PD38 - 120 " ; 122 thru 128 (rev'd to 2000rpm) PD39 - 113 " ; 130 thru 130 (rev'd to 2000rpm) Does this give anyone an idea of what/where I should be looking to correct a recent ongoing problem with poor gas mileage and a noticeable engine miss at idle? Link to comment Share on other sites More sharing options...
Dan Posted March 15, 2004 Report Share Posted March 15, 2004 P017=Left Oxygen Sensor not ready P042=Left Oxygen Sensor Signal Lean Looks like you have a bad oxygen sensor. I prefer to replace them in pairs. You have 2 of them each below both sides the exhaust manifold. They are not hard to replace. You can get them at autozone for about $20-$30 a piece. There is a special tool to remove them, but you can use a 8"-12" crecent wrench. Link to comment Share on other sites More sharing options...
KevinW Posted March 17, 2004 Report Share Posted March 17, 2004 Does this give anyone an idea of what/where I should be looking to correct a recent ongoing problem with poor gas mileage and a noticeable engine miss at idle? I don't think a bad oxygen sensor would cause a bad miss at idle. It is possible a misfire in the left (front) bank is keeping the sensor voltage low (well into closed-loop mode, forcing the DTC). Is this a Northstar or 4.9? In the case of the Northstar, the oxygen sensor has an internal heating element. You could try monitoring PD32 (and compare to PD33) with the ignition on, engine off, first thing in the morning. The reading should start out at 450 mV and gradually fall; this will rule out the PCM, wiring, and sensor. Also, try running a cylinder balance test. ___________________________________________________ Link to comment Share on other sites More sharing options...
anengineer Posted March 19, 2004 Author Report Share Posted March 19, 2004 Thanks to both of you for your response. The past couple days I've been monitoring the PCM outputs: PD32 (ED32) Front Oxygen Sensor Voltage PD33 (ED33) Rear Oxygen Sensor Voltage .....and PD36 (ED36) Front Short Term Fuel Trim PD37 (ED37) Rear Short Term Fuel Trim PD38 (ED38) Front Long Term Fuel Trim PD39 (ED39) Rear Long Term Fuel Trim Two outputs appear abnormal: PD32 - 0 (zero) PD36 - 204 Correct me if I'm wrong but it appears the front oxy censor is feeding back that it is lean to which the short term fuel trim responds by increasing the richness of the fuel mixture. Keep in mind that PD32 is NOT always at zero, it does range, but zero appears quite often and stays there at times for several minutes. When it does range, the outputs favour readings below .45 with occasional jumps above .45; and PD36 also ranges but stays well above 128 most of the time. I'm seeing this as indicating a problem with the front (left bank) oxy sensor causing flooding of the left cylinder bank which is reducing my average mpg and causing engine idle roughness. Anyone else care to offer an opinion? How do you interpret the above output readouts? Link to comment Share on other sites More sharing options...
KevinW Posted March 19, 2004 Report Share Posted March 19, 2004 PD32 - 0 (zero) PD36 - 204 4.9 or Northstar (Concours model)? What is the value of PD32 after a cold soak, engine not running? PD36 = 204 suggests an almost 30% fuel correction. If you suspect the richness in that bank is causing a rough idle, unplug the sensor, reset the PCM memory, then see how it runs. ___________________________________________________ Link to comment Share on other sites More sharing options...
anengineer Posted March 19, 2004 Author Report Share Posted March 19, 2004 I forgot to add readouts from: PD38 (ED38) Front Long Term Fuel Trim PD39 (ED39) Rear Long Term Fuel Trim PD38 - 145 PD39 - 128 Link to comment Share on other sites More sharing options...
anengineer Posted March 19, 2004 Author Report Share Posted March 19, 2004 PD32 - 0 (zero) PD36 - 204 4.9 or Northstar (Concours model)? What is the value of PD32 after a cold soak, engine not running? ..... It's a 4.9. PD32 and PD33 both are .45, cold soak, key on, engine not running. After I start engine, PD32 remains at .45 for several seconds then PD32 drops to zero and PD33 begins ranging. Link to comment Share on other sites More sharing options...
KevinW Posted March 19, 2004 Report Share Posted March 19, 2004 PD32 and PD33 both are .45, cold soak, key on, engine not running. After I start engine, PD32 remains at .45 for several seconds then PD32 drops to zero and PD33 begins ranging. That confirms the 450 mV reference is present. You need to determine if the sensor output is biased low or if a misfire is dumping oxygen in the exhaust stream. I would not expect an intermittent misfire to force the trims over ~40%! A cylinder balance test would help isolate the offending cylinder(s); I would reset the trims first and force open loop. If you unplug the sensor, PD32 should remain at the reference voltage; grounding the signal lead should send it to zero. ___________________________________________________ Link to comment Share on other sites More sharing options...
anengineer Posted March 19, 2004 Author Report Share Posted March 19, 2004 Thanks Kevin. I'll first try disconnecting the oxy sensor leads, reset the trims and see how it responds/reacts. Link to comment Share on other sites More sharing options...
anengineer Posted March 21, 2004 Author Report Share Posted March 21, 2004 Ran the Caddy around for a couple days with the left side(front) oxy sensor harness disconnected. Took a 20 mile trip using cruise control and noticed my average mpg went up from what I had previously been noticing. It wasn't up to what I expected but it was a definate improvement. I also noticed the engine roughness at idle had disappeared. This was enough to confirm the problem as being a malfunctioning oxy sensor. Bought a replacement at Advance Autoparts for a $20 and some change. Got home and while the engine was still hot, pulled the old one and replaced it with the new one. Connected the harness and took it for another test ride. I'm happy to report my average mpg while on cruise control set at 65 mph was hovering around 30 mpg, right back to where it was before I started getting the PO17 and PO42 warnings. The old oxy sensor was fouled with carbon, I'm assuming from the over rich fuel mixture being dumped into the engine's left bank. Thanks to this board and its members I was able to target the problem part instead of willy-nilly replacing parts. Link to comment Share on other sites More sharing options...
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