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Maybe none Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 15 Jul 2009 04:11:48
In Reply to: Which O2 is bad (codes P0125, P0135 & P0141), ToddH, Tue, 14 Jul 2009 06:59:16 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The trouble with fault codes is that people assume that a fault code points to a single part. Fault codes just aren't that good. They give you a starting point to start troubleshooting.
As the esteemed Mr. Bubble says, start with the P0125. Now, that says coolant temp, so you assume a bad coolant sensor. Not always true. You can trigger this fault due to (1) low coolant, (2) a stuck open/bad thermostat, and yes, (3) a bad sensor, or sensor wiring. Check the coolant level. Watch the temperature gauge - is it much lower than normal? In a '97, it rarely reads above 7:30 - but is it reading even lower? Is it taking a long time to get there? If so, it can be a tired thermostat. If the thermostat is over three years old, think about replacing it anyway. (The temp gauge uses a different sensor than the one for the engine control.) Lastly, inspect the wiring to the temp sensor (wedged under the intake manifold). You can test the sensor if you can get onto the leads. With a COLD engine - it should be around 2.1 to 2.9Kohms at 68 degrees F; 1 to 1.3K at 104 F (slightly warm to the touch).
OK, O2 sensor. Interesting that you have both codes. P0135 is for the heating circuit in the front sensor; P0141 is for the heating circuit in the rear sensor. Before you replace both O2 sensors, an expensive proposition, replace fuse 28 (25 amps). If it is blown, well, replace it. If it isn't blown, replace it. I've seen fuses that fail but look OK - they're cheap. Replace it.
After you fix something, you need to clear the code either with your code reader (best way), or by disconnecting the battery lead for about 5 minutes (not as good.) Make sure you've got the radio code!
OK, say the fuse is fine. Since you've got both codes, you'll need to check both sensors, but it is most likely the common power. After fuse 28, a single power signal goes to pin 25 of the big 70 pin connector on the bulkhead. After that, it splits into two and goes to each O2 sensor. Now, it is very unlikely that both sensors have failed (not when you've got one fuse driving both). But to check, pull the connector off each sensor, and measure the resistance across pins 1 and 2. It should be 1.8 to 4.0 ohms. There are four pins on the connector. If you're not sure which pins are 1 and 2, just measure the outside pin and the one next to it, then try the other pair. If one pair is 1.8 to 4.0, you're OK. If neither is, the sensor is bad.
But I'll bet that you've got a stuck thermostat and a bad fuse. Not the same as three bad sensors.
posted by 75.11.4...
, Wed, 15 Jul 2009 04:11:48 <-- Viewing This Message
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