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Testing O2 sensor and A/C microswitch at ECU harness on LH 2.4 200

posted by  jkordzi on  Mon Dec 9 06:53 CST 2002
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last visit: Wed Sep 12 02:43 CST 2001
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I have been trying to track down an intermittant idle/miss and started following the Bentley ECU electrical tests in which you probe the side terminals of the ECU harness (page 241-14). Came across two problems. The first problem is that erminal 15 of the ECU harness and ground should show 1000 ohms with the A/C switch off, and 10 ohms with the switch on. I think my switch or the bulb holder in it is bad because the resistance varies when I try the switch a couple of times. If I swap in another bulb holder (that doesn't light), the resistance is right, but the switch doesn't light. Why would the bulb holder make this difference? When I do engage the A/C the engine rpm doesn't go up, so I thought the problem was in the switch. Any ideas?

My second problem came up when I did the O2 wiring harness test. Bentley says that terminal 24 and ground should show continuity with the O2 sensor connected. I get an open circuit. I traced the green wire from terminal 24 through the firewall to the single black wire of the three wire O2 sensor. Isn't this the wire that caries the data signal from the O2 sensor? Why should this terminal be grounded?






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