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Bought this 2nd hand...on a salvage title. 3 electrical

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Bought this 2nd hand...on...

Bought this 2nd hand...on a salvage title. 3 electrical issues: AC blows cold as desired then kicks off and blows ambient temp air...it's totally unpredictable. Can work for hours then fails or not work at all on start up. Next: The temp gauge on the dash is all over the place. I replaced the ECT, and soldered in a new "stepper" motor for the temp gauge (on instrument cluster) and also, the transmission slips...also unpredictable and intermittent.

Mechanic's Assistant: Have you checked the coolant level? Have you checked for a leak in the radiator?

Yes and yes

Mechanic's Assistant: What is the model/year of your Chevy?

2005 Impala 3400 engine

Mechanic's Assistant: Are you fixing your Impala yourself? What have you tried so far?

I do the work. What Ive tried so far is noted abouve.

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

I said 3 electrical problems, but there is only 2 plus the transmission

Submitted: 8 months ago.Category: Chevy
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Answered in 4 minutes by:
9/26/2017
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago
Jared D
Jared D, ASE Certified Technician
Category: Chevy
Satisfied Customers: 2,244
Experience: Shop Supervisor at County Fleet
Verified

Good morning,

The first thing I would check is the alternator output. Whenever these alternators start to fail it will start cutting off high load circuits at random- like the AC. It will also make the transmission control module act up because it isn't getting a smooth voltage stream.

Do you have a multimeter to check the alternator?

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Customer reply replied 8 months ago
I have one...how do I do this?
Customer reply replied 8 months ago
If calling works easier...but I am in my den and will have to leave to complete the testing....would it work for you to type the steps and I print it out to do the work?
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

With the engine running and fairly warmed up you will set your meter to DC volts. Check either at the post on the back of the alternator with the thick red wire or at the battery terminals (you should get very similar readings, so whichever is easier to access is fine).

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Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

The phone call thing is automated. Not generated by me. I'm fine to continue here- it's cheaper for you anyhow.

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Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

You should see 14-15 volts with the engine running.

Then turn on the highbeams, the AC blower on high, and the radio. The voltage should stay around 14-15 volts. If it drops then the alternator is getting weak.

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Customer reply replied 8 months ago
I am not proficient w/ a multi meter. Each use I have to re read "how to"....so put my + lead on the red at the alt and then ground my black where???
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

Exactly, red wire on the positive terminal black wire on the negative (or any metal spot on the engine or frame).

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Customer reply replied 8 months ago
OK...will take a while as the engine is cold....will get back to you later. Are we working on the AC issue or is this also addressing my temp sensor on the instrument cluster?
Customer reply replied 8 months ago
Are you still with me?
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

It could solve both issues. Irregular alternator voltage can cause all kinds of problems. We'll eliminate that first and if everything looks ok we'll go after the other possible causes of the AC and cluster concerns.

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Customer reply replied 8 months ago
Ok....figure 1/2 hr give or take...thanks
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

Sounds good.

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Customer reply replied 8 months ago
OK...I'm back. The multimeter reads 14.3 to 14.8..so next?
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

That seems ok. Even with everything turned on?

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Customer reply replied 8 months ago
sir...
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

Ok, good. Let's look at the coolant temp sensor. Do you have a scan tool that will monitor the signal from the temp sensor?

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Customer reply replied 8 months ago
Here is what I have done previously....I have replaced the ECT with a new one...and as noted before, I soldered in a new stepper motor on the instrument cluster (twice, as i considered the 1st attempt was a bad one)...What is a scan tool? One of those voltage sensors....to see if current is flowing?
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

A scan tool is a diagnostic computer. They can be a little pricey so if you don't have one, no need to run out and get one.

What exactly does the gauge do?

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Customer reply replied 8 months ago
The guage is all over the place...no response to over response to normal....and different each start up. By the way...I have considered that as the yellow wire (from ECT) goes off under the manifold that perhaps it got pinched in re assembly or is melted....where does it go to actually....we need a schematic probably.
Customer reply replied 8 months ago
I would consider just splicing in a replacement but need to know the routing...
Customer reply replied 8 months ago
Are you researching???
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

I'm trying to find a resistance chart that will help us test the ECT sensor. I can't find one published though. We'll need to know that in order to test the output of the sensor without a scan tool.

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Customer reply replied 8 months ago
Since it's new....it's going to be working properly, isn't it?
Customer reply replied 8 months ago
I am going to copy/paste something I found...ngine Coolant Temperature (ECT) Sensor
Print
OPERATIONThe Engine Coolant Temperature (ECT) sensor is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant stream. Low coolant temperature produces a high resistance (100,000 ohms at -40°F.) while high temperature causes low resistance (70 ohms at 266°F.). The PCM supplies a voltage (about 5.0V) through a pull up resistor to the PCM's ECT signal circuit and measures the voltage. When the engine coolant is cold, the sensor (thermistor) resistance is high, therefore the PCM will measure a high signal voltage. As the engine coolant warms, the sensor resistance becomes less, and the ECT signal voltage measured at the PCM drops. With a fully warmed up engine, the ECT signal voltage should measure about 1.5-2.0 volts. By measuring the voltage, the PCM calculates the engine coolant temperature and engine coolant temperature affects most systems the PCM controls.A technician's scan tool displays engine coolant temperature in degrees. After engine start up, the temperature should rise steadily to about 195°F (90°C), then stabilize and the thermostat opens. If the engine has not been run for several hours (overnight), the engine coolant temperature and intake air temperature displays should be close to each other. A hard or even an intermittent fault in the engine coolant temperature sensor circuit will set a hard Diagnostic Trouble Code (DTC).Most ECT sensor also contain another circuit which is used to operate the engine coolant temperature gauge (if equipped) located in the instrument panel.TESTING
Customer reply replied 8 months ago
That last statement gives me the idea that maybe the circuit on the circuit board may be cracked or damaged....make any sense to you?
Customer reply replied 8 months ago
ie circuit on the circuit board on the instrument cluster ...
Customer reply replied 8 months ago
does the yellow wire from the ECT run directly to the cluster or does it go to the ECM/PCM?
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

It should be good, since it's new, but I've seen them defective straight out of the box.

The problem could very well be somewhere in the instrument cluster.

When you first turn the key on without starting the engine do the gauges perform a sweep test where all of the gauges go all the way up and then all the way down.

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Customer reply replied 8 months ago
I think so....will go check quickly...meantime can you check the routing of that yellow wire? I'll be right back..
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

Have you attempted to bleed the cooling system yet? If there was an air pocket in the cooling system the temp gauge would act up and the AC would stop working intermittently.

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Customer reply replied 8 months ago
There are 3 needles....fuel, speedometer, and the temp. The fuel moves to it's proper position...the speedometer stays still...and the temp sensor is unpredictable...
Customer reply replied 8 months ago
How is a bleed accomplished? And how likely is this air pocket notion. I recently drove a 12 hour trip, and the AC would wokr for hours at a time. Wouldn't normal cycling have produced the fault if a pocket existed?
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

In that case it's pretty likely that the instrument panel is the problem. All of the gauges should sweep all the way up and then back down.

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Customer reply replied 8 months ago
even the speedometer??
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

Even the speedometer.

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Customer reply replied 8 months ago
are you saying the temp gauge is somehow causing the AC to shut down?
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

Not necessarily. Low coolant levels or irregular signals from the body control module saying the engine is overheating will make the AC turn off.

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Customer reply replied 8 months ago
I am still kind of interested in replacing the yellow wire out of the ECT, but I need to know the routing...can you help with that? do you have a schematic? What is the "body" control module? the ECM or PCM?
Customer reply replied 8 months ago
By the way...it isn't a low coolant issue....that's been checked.
Customer reply replied 8 months ago
Are you still there??
Customer reply replied 8 months ago
Thank you Jared. I'll pursue some other options...Appreciate your effort.
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

I've looked over every diagram. Unfortunately GM expects you to be able to check it with a scan tool.

The wire from the sensor goes through the harness to the body control module where it is translated into a signal for the gauge.

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Customer reply replied 8 months ago
What is the body control module? The PCM...the power control module?
Customer reply replied 8 months ago
If that's the case then I will do a replacement routing directly to the PCM,...as I suspect there is something wrong after it goes
under the manifold.
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

The BCM is the body control module. It works along with the PCM to run everything not ignition related. That means all of the sensors, accessories, etc.

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Customer reply replied 8 months ago
OK...thank you
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

I also controls the AC- With a scan tool you can command the BCM to run the AC, test the gauges, etc. From there you can determine what part is faulty.

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Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

Please let me know if you need additional info.

* Please take time to rate my response- as an expert I don't work directly for Just Answer- any resources I provide to you are furnished at my own personal expense. I only receive compensation based on positive ratings from you. Therefore, I cannot offer my time, insights, advice, diagrams, etc, without that positive rating. If you are unable to positively rate my response please let me know. After rating I will still be available for follow-up questions at no additional charge.

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Customer reply replied 8 months ago
I am puzzled as to how I should respond. As we could not identify the problem or a solution a top rating wouldn't seem appropriate. But neither would I wish to ding you with a negative as you were obviously making efforts. So a "no call" seems the better choice.
Chevy Mechanic: Jared D, ASE Certified Technician replied 8 months ago

I'm still here to help as needed. Just hadn't received a response in a couple of days so I thought maybe you had resolved the concern.

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