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Tech Solves Altima's Power Window ProblemPosted 7/9/2004By Paul Kujawa
A 1993 Nissan Altima had power window problems. You could not operate the front passenger or the two rear windows. However, the driver's window worked normally. You would expect it to be simple enough to fix. The customer probably inadvertently pushed the power window lock button in the main switch, preventing all passenger windows from operating. Unfortunately, this was not the case. The power window switches in each of the passenger doors were also tried, and the windows were still inoperative. System operation: Each passenger door has a power window switch and a power window amplifier. The power window amplifiers control the power window motors in each passenger door. These amplifiers reverse power and ground, allowing the passenger windows to go up and down, based on signals from their respective power window switch in the door, or from the main switch via data signals. The main switch directly controls the driver's power window motor and sends data (command) signals to each of the amplifiers, enabling all the windows to be controlled from the main switch. The main switch can "lock out" all passenger windows with a separate signal when the power window lock button is "on" so the windows cannot be operated from individual door switches. When the power window lock button is on, the power window lock signal voltage should be near 0 volts. When the power window lock button is off, the power window lock signal voltage should be approximately 12 volts. The main switch and each of the power window amplifiers receive a constant battery voltage supply on a white/red wire that comes from a fusible link from the battery through a circuit breaker. There is also a black ground wire at each of the power window amplifiers. Back to the 1993 Altima. Since the driver's power window worked OK, we knew that the main switch was receiving battery voltage from the white/red wire, meaning the fusible link and the circuit breaker were good. When the technician accessed the power window amplifiers on the passenger windows, he noticed burn spots inside the amplifiers. He replaced all three amplifiers and the windows seemed to work fine. The customer picked up the vehicle. But it wasn't long before the Altima returned with the same problem. The technician checked the amplifiers, and once again found burnt spots. That's when he decided to call our hot line. Something was burning up a power window amp. My first thought was excessive current flow from a defective power window motor, but the likelihood of three defective power window motors taking out all three power window amplifiers is slim. Another consideration: Had the battery been connected or jumped backward? There was no evidence of this, and all other electrical systems on the vehicle functioned normally. I suggested that the tech do some voltage testing at one of the power window amplifiers to check for any abnormal readings. Battery voltage supply on the white/red wire at the power window amplifier tested OK. A voltage drop test performed on the black ground wire also tested OK. The power window could be operated by applying power and ground to the motor to make the window go down, and reverse the power and ground to the motor to make the window go back up. There was also battery voltage on the power window lock signal from the main switch (also a white/red wire, not to be confused with the power supply) so the power window lock switch was off. Checking the data signal line from the main switch revealed voltage even though the main switch was not in operation. Typically, a normal working system has approximately 12 volts on the data signal line from the main switch to signal a given power window amplifier to command the window to go up. Voltage should read about 4 volts on the data signal line to a given power window amplifier to command the window to go down, and 0 volts (or near zero) when there is no window operation. This vehicle had approximately 8 volts on all three data signal lines, causing the power window amplifiers to continue to try to operate the windows, and it burned out the amplifiers. Power window amplifiers that continuously buzz (before they burn out) can also be an indication of this problem. In this case, the vehicle had a defective main switch. After the switch was replaced (along with three more power window amplifiers), the tech verified that the data signals had 0 volts when the main switch was not being operated. Problem solved!
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