Tip & How-To about Nissan Maxima

Nissan Maxima Ground Fault


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Several months ago my daughter in law, Wendy, brought her 2000 Nissan Maxima to me with a problem. The CEL (check engine light) was on. Using an OBDII code machine I discovered two codes; P0420 and P0430 were causing the CEL to be on. Vehicles manufactured after 1995 use On Board Diagnostics II. Prior to that year On Board Diagnostics I (OBDI) was the standard. Both of these codes indicated that the oxygen sensors, located upstream and downstream, on the catalytic converter assembly were defective. These sensors are designed to keep tabs on the health of the converters. The two codes are saying the sensors, not the converters themselves, are faulty.

Automobiles of every make and model seem to push these codes on a regular basis. I have often wondered if O2 sensors are really bad. Sensors can cost as much as $130. Replacing two, only to find that your car's computer still sees them as faulty makes you want to kill the messenger. "Perhaps I can clean them", I thought. However Wendy is convinced that I should replace both sensors. After a coffee I have her whittled down to one sensor; "The front one", I tell her, "The easy one".

O2 sensor changed, I clear the CEL light by disconnecting the positive battery cable; Reconnecting one coffee later. I expect it to come back on, telling me the other one is still defective. I should be so lucky.

Three days later she's back; Sadly I see both sensors are still bad. An under car inspection reveals the rusted remains of a very narrow ground strap hanging from the rear catalytic. Then it occurs to me that ground straps were not visible under the hood. Using an ohm meter (purchased at Home Depot for $10.98) set on the X10 scale, I measure from engine block to body and body to the negative battery terminal. Making sure I have bear metal to touch my probes to. I'm looking for zero ohms (full needle deflection). But that is not what I read. Mr. Meter is showing 280 (X10)= 2,800 ohms. This is not good.

Using 8 gauge stranded wire I assemble two straps, both 18" in length. On one strap I solder an eyelet (large enough to accept the bolts I have selected) to both ends. This strap connects to the left side of the radiator mounting bracket. The other end, on the left side of the engine to a bolt which holds a bracket in place. Next I repeat the process with one exception. The end which connects to the negative battery terminal is somewhat larger; Also it needs to be connected on the outside of the of the cable connector. Then the other end connects to the right side radiator bracket bolt.

I start the engine and the CEL light is out, and no rough idle; "Always rough idled", observes Wendy. Several weeks later Wendy says "my gas mileage is killer"! When asked what did you measure? All I get back is a blank stare; Some things never change.

Over the next four months I work on three more; A 2001 Maxima, a 2003, and another 2000. All three have a variety of codes but respond to ground strap installation. All three now run code free and idle like cream cheese is smooth.

I stumbled upon a fix for a common fault; One that saves a lot of money. Being able to share this tip is very satisfying, very satisfying indeed. Now if I can only teach Wendy how to measure gas mileage. Expect a miracle I'm told.


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