Hello everyone!

I have a 1994 mazda protege with some issues. First issue.

1. The sensor that turns the cooling fan on doesn't seem to work.(located in the thermostat housing) If I unplug the sensor and ground it out, the fan comes on. (so I bought a new sensor still no luck)

2. I failed the low speed emissions testing due to High HC and NOx.

I have no Service engine light.
STD. Actual
HC(ppm) 141 217 FAIL
CO(%) .79 .51 PASS
CO2 15.0
O2 .8
NOx(ppm) 1088 2474 FAIL
Dilution(%) >6 15.5

So far I've replaced the O2 sensor, air filter, fuel filter, changed oil, and replace cooling fan sensor (in thermostat housing). going to retest tomorrow.

I have a funny feeling my PCM is half way working. I disconnected my O2 sensor and drove around trying to get my SES light to come on. I even disconnected a spark plug wire by accident and ran it on 3 cylinders. Still no SES light. Is my guess correct? faulty PCM? pin 10 and GND doesn't activate SES light.

TIA,

Q

 

ECU failures were pretty rare on those but not unheard of. If the thermostat is stuck open it may not get hot enough to turn the fan on and that would cause emmisions problems. A slight head gasket leak can cause an air pocket at the sensor and cause a low reading. As far as failing emissions try a bottle of Techron in the gas tank to decarbon it and clean the injectors up. Be sure to use NGK spark plugs.
Some systems require 3 driving cycles with a failure to set a check engine light/code but is the light on with just the key on? Could have a blown bulb or could have been removed.

 

The thermostat is newish. I replaced it a couple of months ago. Can't remember the heat range on it but it is one of those that does have the little hole in it to bleed air and also suppose to have some overheating feature that prevents it from being stuck.

I'll try the techron and NGK plugs.

The bulb works, I can turn the key to the on position without the car running and the bulb will be on. I tried pulling codes using the TEN and GND and the light didn't flash whatsoever. Heck I would hope that it would've at least came on with the plug wire disconnected.

Thanks.

 

Boy! Another one straight out of the twilight zone!
Technical issue #1: The fan thing; try the acid test. On a warm day, block off the rad. by sliding a piece of cardboard down the rad mounting guides, then drive around a bit until the temp. gauge crawls above the mid range mark, stop, and let the car idle. The cooling fan should cut in. If it doesn't, pull the cardboard and allow the engine to cool down and follow the trail from there.
Technical issue #2: Emissions etc. Your car pre-dates the OBD-II standards for emissions, and OBD-II compliance requirements vary from jurisdiction to jurisdiction, so your vintage of vehicle may or may not have to meet the norms currently applicable.
You should find a sticker somewhere under the hood which, among other things, specifies exactly what OBD specification applies to your vehicle, and it should be tested according to that spec. not necessarily to the current OBD-II spec.
This would also explain why you got an OBD-II fail, yet have no MIL (CEL) light on.
Beyond this, you have to consider the state of your MAF sensor (the old vane or flap type I think), your main inlet air duct (hidden cracks), your idle air control valve (IAC), and especially your exhaust gas recirculation control valve (EGR) and its possibly blocked tubing.
Judging by the numbers and the fact you don't mention any particular symptoms of misbehavior, I think your wheels are still good for a few more ZOOM ZOOMS yet.

 

Ok...thanks for the tips. I'll get cracking on these issues this weekend.

As far as the cooling fan. That connector that plugs into the sensor located in the thermostat housing broke. "old and brittle" I guess. Anyway, since its a 1 wire prong, I simply slid it onto the male prong in the sensor. My understanding of the way the sensor works is at a certain temperature, the sensor will cause the wire to ground out and therefore kick the cooling fan on.

I'm also filling out the paperwork for either repair assistance or a waiver since I've recently joined the unemployed ranks!