Low volume on radio, I replaced the amplifier with an used one, but the problem still present. All channels are Ok.

What system does it have ? Base or up level ,does it have a amp ? Do you know what a RPO code is ? Without testing no one could say for sure what the issue is . First off would need to know what system we are dealing with .
RPO Options
The entertainment system on this vehicle is configured with either a base or uplevel audio system. Both the base and uplevel audio systems contain a radio, antenna, and speakers.
The following shows the Enteratinment RPOs that are available for this vehicle:
• (UM7) AM/FM Stereo
• (U1C) AM/FM Stereo CD
• (US8) AM/FM Stereo, CD, MP3, RDS, EQ
• (US9) AM/FM Stereo, 6-Disc CD, MP3, RDS, EQ
• (UXQ4) Base Four Speaker
• (U79) Uplevel Four Speaker
• (WBM) Premium Audio
• (U2K) Digital Radio

Circuit Operation
Radio Power: The main radio power is supplied by the 10A RADIO (BATT1) fuse in the body control module (BCM). Radio switch-on power, 12 volts in ACC, RUN or RAP, is supplied by the 10A RADIO (ACC.) in the BCM.
Radio Grounds: The main radio ground provides a ground for the radio circuits. An additional braided ground strap provides a shielding radio case ground to reduce EMI noise. Both grounds are connected together inside the radio.
Radio Speaker Outputs: At zero volume, the plus (+) and minus (-) speaker outputs are both approximately 5-6 volts, measured to vehicle ground. If a plus or minus for any speaker output is shorted to ground or voltage, the radio circuitry will turn OFF all 4 speaker outputs for component protection. Above zero volume, the plus and minus change to create a voltage difference between each other, to drive the voice coil of the speaker.
Radio Park Lamp Input: The radio park lamp input allows the radio to sense when the vehicle parking lamps are ON. When the parking lamps are ON, this circuit goes to battery voltage, and the radio display back-lighting switches from full bright to the brightness level determined by the I/P illumination input.
Radio I/P Illumination Input: A pulse width modulated (PWM) voltage for instrument panel (I/P) illumination is provided to the radio I/P illumination input. The Radio uses this input to directly illuminate the radio buttons and adjust the radio display back-lighting when the park lamp input is ON.
Amplifier Power: The main amplifier power is provided by the 20A PREM AUDIO fuse in the instrument panel fuse block..
Amplifier Radio Speaker Inputs (WBM only): The radio speaker outputs, at a reduced output level for amplified systems, are the amplifier inputs. The amplifier boosts these inputs and outputs them to the vehicle speakers. Speaker plus and minus circuits from the radio change to create a voltage difference between each other. If one speaker plus or minus is open between the radio and the amplifier, the input to the amplifier is approximately half because only one of the circuits is changing. The speaker for that channel then operates at approximately only half the normal volume.
Amplifier Speaker Outputs (WBM only): At zero volume, the plus (+) and minus (-) speaker outputs are both approximately 5-6 volts, measured to vehicle ground. If a plus or minus for any speaker output is shorted to ground or voltage, the amplifier circuitry will turn OFF either the front outputs or rear outputs for component protection. Above zero volume, the plus and minus change to create a voltage difference between each other, to drive the voice coil of the speaker.
Amplifier Radio-On (WBM only): When the radio is ON, this circuit is pulled to 12 volts by the radio. The amplifier switches ON when this circuit is 12 volts and switches OFF when this signal is 0 volts.
Remote Radio Audio Signal Inputs (UE1 only): Audio output from the OnStar® communications module connects to the remote audio signal inputs of the radio. When the cellular telephone mute signal goes to 0 volts, the radio over-rides any other audio signal and uses these inputs as the source for output to the speakers.
Cellular Telephone Mute (UE1 only): The OnStar® communications module uses the cellular telephone mute signal circuit to over-ride the radio for OnStar® communication. When cellular telephone mute is not active, this circuit is held at 2 volts by the radio. When the cellular telephone mute signal is pulled to ground, the radio over-rides any other audio signal and uses the remote audio signals as the source for output to the speakers. If the radio was OFF when this circuit is pulled low, the radio will turn ON. Additionally, the radio fades the speakers to full front, adjusts the volume to an initial audible level, and sets an AutoTone designed for optimal use with OnStar®. When the mute signal is no longer pulled to ground, the radio returns to the mode it was in previously.

Hooking up a professional or factory scan tool that can read radio codes would be one of the first test's to do .
DTC B1025, B1035, B1045, or B1055 (w/out RPO WBM)
DTC B1025, B1035, B1045, or B1055 (w/ RPO WBM)
DTC B1030, B1040, B1050, or B1060 (w/ out RPO WBM)
DTC B1030, B1040, B1050, or B1060 (w/ RPO WBM)
DTC B1259
The following conditions are present for 250 ms or longer:
B1025 - B1055 01
One of the speaker positive output circuits is shorted to battery.
B1025 - B1055 02
The speaker positive output circuit is shorted to ground.
B1025 - B1055 04
The speaker positive output circuit is open.

Your best bet , take it to a qualified repair shop .

Which of these does your truck have ?
The Entertainment System on this vehicle is configured with a radio, antenna, and speakers.
The following list shows the radios available for this vehicle:
• Radio (UM7) - AM/FM with Cassette
• Radio (UB0) - AM/FM with CD
• Radio (UB1) - AM/FM, Cassette and CD
• Radio (UC6) - AM/FM, Integral Multi Disc CD Changer
Audio Amplifier
The audio amplifier is standard on some vehicle lines but is optional on most. The radio supplies low level audio signals to the audio amplifier in order to boost the signal sent to the speakers. The class 2 signal circuit allows the radio to recognize that an amplifier is present. Once the radio detects an audio amplifier, it will output low level audio signals. The audio amplifier is turned on when it receives a message via the class 2 serial data circuit indicating that the radio is on.
Digital Radio Receiver
The radio communicates with the digital radio receiver via the class 2 communications circuit. The digital radio receiver sends low level audio signals to the audio amplifier.
Steering Wheel Controls
Some audio functions are available using the steering wheel controls. The steering wheel controls consist of multiple momentary contact switches that connect a series of resistors. When a steering wheel control button is pressed, a specific resistance value is noted by the body control module (BCM). This results in a generated voltage, unique to the particular button. The BCM alerts the radio that the button has been pressed, and the radio responds, just as if the corresponding radio front panel button had been pressed.
Amplifier
The amplifier in early build vehicles is a class 2 device that communicates with the scan tool on the Class 2 bus. The Class 2 amplifier will set a U100 in the radio if there is a communication problem. The late build vehicles have a NON-Class 2 amplifier that does not communicate over the Class 2 bus and therefore the NON-Class 2 amplifier will not set codes. Both amplifiers have similar operating characteristics, therefore, there are not separate diagnostics for the NON-Class 2 amplifier.
Circuit Description
When the radio is powered up, the radio supplies low level audio signals to the speakers. If the vehicle is equipped with an audio amplifier, the amplifier will boost the signal sent to the speakers. The radio tests the speaker output circuits for a short to voltage or ground.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
• DTC B1025 Audio Output 1 (Left Front) Circuit
• DTC B1035 Audio Output 2 (Right Front) Circuit
• DTC B1045 Audio Output 3 (Left Rear) Circuit
• DTC B1055 Audio Output 4 (Right Rear) Circuit
Reduced Volume - One or More Speakers
Step
Action
Yes
No

Schematic Reference: Radio/Audio System Schematics

1
Did you perform the Diagnostic System Check - Vehicle?
Go to Step 2
Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
Turn ON the ignition, with the engine OFF.
Turn ON the radio.
Adjust the radio balance and fade controls to each speaker.
Do all of the speakers operate properly?
Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
Go to Step 3

3
Turn the ignition ON, with the engine OFF.
Adjust the volume level.
Test the appropriate speaker output circuits of the radio for A/C voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did the A/C voltage fluctuate with the audio output?
Go to Step 4
Go to Step 8

4
Turn OFF the ignition
Disconnect the radio.
Test the appropriate speaker output circuits of the radio for high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 9
Go to Step 5

5
Inspect for poor connections at the harness connector of the radio. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Did you find and correct the condition?
Go to Step 9
Go to Step 6

6
Inspect for poor connections at the harness connector of the appropriate speaker. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 9
Go to Step 7

7
Replace the speaker. Refer to Speaker Replacement Reference .
Did you complete the replacement?
Go to Step 9
--

8
Replace the radio. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.
Did you complete the replacement?
Go to Step 9
--

9
Operate the system in order to verify the repair.
Did you correct the condition?

Speakers get power from the amp if your system has one or from the radio , if the tweeters work it's not a fuse problem . You like listen to your stereo loud . Blew a channel in the radio or amp ?
Take it and have it checked for DTC'S - diagnostic trouble codes
DTC B1025 01: Audio Output 1 Left Front Circuit Short to Battery
DTC B1025 02: Audio Output 1 Left Front Circuit Short to Ground
DTC B1035 01: Audio Output 2 Right Front Circuit Short to Battery
DTC B1035 02: Audio Output 2 Right Front Circuit Short to Ground
DTC B1045 01: Audio Output 3 Left Rear Circuit Short to Battery
DTC B1045 02: Audio Output 3 Left Rear Circuit Short to Ground
DTC B1055 01: Audio Output 4 Right Rear Circuit Short to Battery
DTC B1055 02: Audio Output 4 Right Rear Circuit Short to Ground

Each of the audio output channel circuits (+) and (-), at the radio and audio amplifier (if equipped) have a DC bias voltage that is one half of the battery voltage. When using a DMM, each of the audio output channel circuits will measure approximately 6.5 V DC. The audio being played on the system is produced by a varying AC voltage that is centered around the DC bias voltage on the same circuit. The AC voltage is what causes the speaker cone to move and produce sound. This voltage will vary depending on what type of audio is being listened to, talk or music, and type of music, as well as the volume setting of the system. Low volume and talk settings will measure around 1V AC and less, where constant music may measure 3 V AC and slightly higher.
Do you know how to do DC voltage testing ?
Without Amplifier without UK6
Ignition OFF, disconnect the harness connector at the appropriate speaker.
Radio ON, test for 5.0-7.5 V between the signal circuit terminal A and ground.
? If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the radio.
? If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the radio.
Test for 5.0-7.5 V between the signal circuit terminal B and ground.
? If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the radio.
? If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the radio.
If all circuits test normal, replace the speaker.

Maybe a shorted speaker causing the power amplifier inside the radio to shut down or a speaker wire shorted to chassis and last the internal amplifier of the radio cd set faulty by itself... set volume to zero power it off take out the radio cd set; remove the speaker iso plug leaving the power plug only in and power it on if necesary turn again the volume down to zero and wait if it keeps turned on it a speaker problem if it shut itself off again then you go for a repair or a new one

Check all your fuses under the dash and under the hood, replace any blown fuses you find. Sometime the car makers put 2 or 3 fuses in different locations for the same unit. If everything seems ok, then I'd say when you used jumper cables, if the radio was powered on at the time you may have blown the amplifier and it would be time to replace the radio.

The chimes an turn signal noise come out driver door speaker . Both front speakers not working could be a blown circuit fuse inside the radio or just blown front speaker channel . Your best bet , take it to a GM dealer or someother qualified repair shop . You have no idea of the complexity of this . The radio can set DTC'S - diagnostic trouble codes , believe it or not !
DTC B1025, B1035, B1045, or B1055
DTC B1025 01: Audio Output 1 Left Front Circuit Short to Battery
DTC B1025 02: Audio Output 1 Left Front Circuit Short to Ground
DTC B1035 01: Audio Output 2 Right Front Circuit Short to Battery
DTC B1035 02: Audio Output 2 Right Front Circuit Short to Ground
DTC B1045 01: Audio Output 3 Left Rear Circuit Short to Battery
DTC B1045 02: Audio Output 3 Left Rear Circuit Short to Ground
DTC B1055 01: Audio Output 4 Right Rear Circuit Short to Battery
DTC B1055 02: Audio Output 4 Right Rear Circuit Short to Ground

Each of the audio output channel circuits (+) and (-), at the radio and audio amplifier have a DC bias voltage that is one half of the battery voltage. When using a DMM, each of the audio output channel circuits will measure approximately 6.5V DC. The audio being played on the system is produced by a varying AC voltage that is centered around the DC bias voltage on the same circuit. The AC voltage is what causes the speaker cone to move and produce sound. This voltage will vary depending on what type of audio is being listened to, talk or music, and type of music, as well as the volume setting of the system. Low volume and talk settings will measure around 1V AC and less, where constant music may measure 3V AC and slightly higher.
DTC B1287 01: Amplifier Control Signal Circuit Short to Battery
DTC B1287 02: Amplifier Control Signal Circuit Short to Ground
DTC B1287 04: Amplifier Control Signal Circuit Open

The radio provides a remote amplifier mute output circuit to control overall muting of the remote amplifier. The amplifier receives pulse width modulated (PWM) signals on the control circuit at varying duty cycle percentages for controlling muted and unmuted functions of the amplifier. Circuitry internal to the radio monitors the remote amplifier mute circuit for faults and sets the appropriate DTC when faults are detected.

If you are replacing the factory radio with this there are two issues that could be causing you grief. First, the radio only has 14 watts RMS power output. This is rather low by standards. Additionally, that is factored into a 4-ohm speaker load. Chances are that the factory speakers are 8-ohm, which will cause further loading. You should consider replacing the speakers with 4-ohm and possibly add an amplifier to the system to achieve optimal performance.

If your asking about the radio DTC this is what it is

Circuit Description

When the radio is powered up, the radio supplies low level audio signals to the speakers. If the vehicle is equipped with an audio amplifier, the amplifier will boost the signal sent to the speakers.
Conditions for Running the DTC

The test is performed when the radio switches from OFF to ON. The radio will continue to test for the fault once every 0.5 seconds.
Conditions for Setting the DTC

The radio sets a current status for this DTC when a short to ground or voltage is detected on any of the speaker channels for 1.5 seconds.
Action Taken When the DTC Sets

No sound is present from one or more of the speakers.
Conditions for Clearing the DTC

The fault condition is not present for 5 seconds.

What to do:Test the speaker outputs from the radio for short to ground or voltage. Inspect for poor connections at the harness connector of the radio. Reprogram the radio. Replace the radio.

Try to check the wire connection, you may have a lose wire

Radio is bad,replace it,it is the only thing you can do to solve the problem.