CODE AO 12 1995 STS

[iamthewaz]

Changed this sensor 5 times. But still after starting and stopping car ac craps out. But at initial start ac works ice cold everytime. Does anyone know could it also be ambient outside air temp sensor . Is ther away t troulble shoot this sensor

[Cadillac Jim]

A012 Low Side Temperature Sensor Circuit

Apparently there is a problem with the connector, or perhaps the wiring harness. Do you have any other codes? Are you reading them through the HVAC buttons and the DIC, or a code reader?

[Cadillac Jim]

I got an email reply from the post I put here. I use Caddyinfo for helping other people with Cadillac troubleshooting because lots of other people smarter than me see my post and can jump in if I left something out or got it wrong, and when we succeed in helping someone the way we did it goes into our collective database. So, I'll reply here.

From the email:

I replaced the connector on the sensor. Every morning the ac works excellent then after about the third time starting and stopping the car that dam ao12 and warm air. Can it possibly be the outside ambient temp sensor is bad could it be the culprit. Seems like someone had a similar problem in the past. If you get in the car the first start after sitting all night the ac will continue to blow cold all the way from new york to florida . but shut the car off about the third time thats it ao12. Sorry about the run on sentences. if you have any idea I would greatly appreciate it.

I'm sorry, I thought you said that you changed the *sensor*.

The set of diagnostics in my OBD I list for the A/C is pretty short. It does have one for outside temperature sensor, so I don't think it's likely that another sensor or its wiring would cause the A012. What might be doing it is low Freon, not low enough to set the low Freon codes A046, A047, or A048. I'm saying this because you get the code after starting and stopping a few times, and the low-pressure side may be frosting over.

Someone with an shop manual that gives the logic that sets A012?

[Cadillac Jim]

Another email reply:

... freon pressure is perfect low pressure sensor replaced and new connector spliced in. mixer door working fine. So heres the deal initial start in morning air is ice cold ., and will stay ice cold ,untill you stop and start car a few times. then the dam ao12 back again . the lines are not freezing up either . also replaced outside ambient air tremp sensor . So what in the world could it be .

A012 Low Side Temperature Sensor Circuit

I don't have a shop manual that will tell me the details of an OBD I DTC. No one stepped up that has OBD I experience or manual as of yet. I would venture that A012 corresponds to the OBD II DTC

B1321 A/C Low Side Temperature Sensor Fault

My FSM doesn't specifically deal with this DTC. On page 1B-32 I see that the low-side and high-side sensors are on either side of the orifice tube, which is against the firewall high on the passenger side just before the freon line goes through the firewall to the evaporator. In my FSM troubleshooting charts for A/C operation, the first question is whether the compressor is running or not. I'll assume that it doesn't run because the DTC will tell the ACM to turn off the compressor and that this is why you don't get cold air. But then, the FSM says to clear any DTCs by finding the problem and fixing them as the first step. You know from the A012 that the circuit to the low side sensor is giving trouble.

The low side sensor is a thermocouple that is inserted into the freon; unscrewing this sensor will bleed down the system. Sensors rarely go bad so I wouldn't go there unless you had hard proof that the sensor was bad from an ohmmeter. I don't have the wiring harness diagram for that connector in front of me but I would assume that the sensor connector has two terminals, and that the wire is a twisted pair. YOu can check the resistance between the terminals on the sensor and it should be under 10 Ohms (perhaps much smaller) and there should be no short to ground from either of them; if there is only one wire it should have a few Ohms resistance but not a short circuit. If that checks good, That leaves the connector and wiring harness.

I think the most likely culprit is the connector. Make sure that the wiring harness isn't binding so that engine movement during driving isn't pulling on the connector. Also, make sure that condensation from the freon line isn't running into the connector and shorting the contacts to ground.

You might also check your torque wishbones and your front motor support to make sure that your engine isn't moving excessively when you drive.