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Unexpected evening of fun; Problem was O2 Sensor ground Posted by TonyJ [Email]  (#407)  [Profile/Gallery]
(more from TonyJ) on Sun, 21 Nov 2004 20:20:35
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My wife called to report that the Aero's check engine light was on after it didn't start on the first try. She drove home 25 miles with no problem. I checked for flash codes and found 6: O2 sensor. One of the checks in the TRIONIC manual that can be done without an isat is to verify that the outer shell of the O2 sensor is grounded. I measured ~3K ohms..eureka! an easy fix.
It appeared that the high resistance was between the down pipe and the turbo housing, so I replaced the top/front 8mm nut, which looked very rusty. Lots of PB blaster, expletives, and finally a dreml cut-off wheel were needed to remove the nut. I wire brushed everything and used a stainless nut and split lockwasher to dig in for better contact, but nothing changed!
After a few more attempts to improve the contact, I decided that the problem must be in the O2 sensor threads, which the manual suggests you remove and wire brush. After looking an the incredibly difficult routing of the cable and the insane location of the connector near the bottom of the dipstick tube and not wanting to risk damaging the $189 sensor, i decided to go for a temporary quick fix. I wrapped #12 solid copper wire around the sensor shell, clamped it with a stainless hose clamp, and connected the other end throug a lug to one of the A/C compressor mounting bolts. The resistance became 0,1 ohms. I reset the ECU by unplugging it for >5 minutes, took it on a run up I495 for a little adaptation, and the check engine light remains out.
I am left with a few questions. Are the 8mm nuts anything special for the high temperature? Will stainless steel be OK? Why didn't Saab forsee this grounding problem and add a parallel circuit?
TonyJ
94 Aero 5 sp. 93K
97 CSE turbo 5 sp. 89K
posted by 24.34.16...
, Sun, 21 Nov 2004 20:20:35 <-- Viewing This Message, Tue, 23 Nov 2004 03:57:23
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