Bypass stuck open

While in freeze mode check the hot gas valve temperature on the feed side and on the opposite side of the valve if it is the same temperature then it is bypassing. also the evaporator coil will be warm to the touch.

causes could be - Faulty Vacuum hoses damaged
- Faulty Air Pump inoperative
- Air bypass solenoid harness is open or shorted
- Air bypass solenoid circuit poor electrical connection
- Air bypass solenoid leaking/blocked or stuck open/closed
- Air diverter valve leaking/blocked or stuck open/closed

An air pump is used on the vehicle to lower tail pipe emissions on start-up. The Powertrain Control Module (PCM) grounds the Air pump relay control circuit which energizes the Air pump. The PCM also grounds the Air combination valve vacuum control solenoid circuit, which energizes the Air vacuum control solenoid. Vacuum is then applied to both Air combination valve diaphragms which opens the shut off valves. The PCM enables both circuits simultaneously when Air system operations id desired. When the AIR system is active, then Air pump forces fresh air into the exhaust stream in order to accelerate catalyst operation. The AIR combination valves replace the conventional check valves. When the AIR system is inactive the shut off valves prevent air flow in either direction.

If you are getting pressure at times that would seem to indicate that the pump is till ok. There is a pressure bypass valve that operates when you let go of the trigger - it does not let internal pressures build up monumentally when you release the trigger........if this valve gets stuck in the open position the pressure is reduced considerably because of the bypass path. Unclog it, clear it. or replace the valve to restore normal operation.

Since the heater fires it sounds like it could be the bypass valve stuck open. The bypass valve allows some of the water to enter the heater, while the rest bypasses the heater and returns to the pool.


If the bypass is stuck open, or broken, it allows the vast majority of the water to bypass the heater and continue to the pool. The water that is in the heat exchanger will become too hot due to slow flow and activate the high limit switch, turning the heater off.


The bypass is located where the pipes attach to the heater and can be checked or replaced if needed fairly easily.

you may have a clogged heater core or heater core bypass valve may be stuck closed. bypass valve is usually on the firewall on one of the heater core hoses. if valve seems to be operating properly. you will need to let the vehicle cool down. disconnect both heater hoses. connect garden hose to one side of heater core let water run through one side and then the other side. if the heater core is too clogged it may need to be replaced.

Here is the definition of the code.

P0410 GMC Description An air pump is used on the vehicle to lower tail pipe emissions on start-up. The Powertrain Control Module (PCM) grounds the Air pump relay control circuit which energizes the Air pump. The PCM also grounds the Air combination valve vacuum control solenoid circuit, which energizes the Air vacuum control solenoid. Vacuum is then applied to both Air combination valve diaphragms which opens the shut off valves. The PCM enables both circuits simultaneously when Air system operations id desired. When the AIR system is active, then Air pump forces fresh air into the exhaust stream in order to accelerate catalyst operation. The AIR combination valves replace the conventional check valves. When the AIR system is inactive the shut off valves prevent air flow in either direction.
Possible causes - Faulty Vacuum hoses damaged
- Faulty Air Pump inoperative
- Air bypass solenoid harness is open or shorted
- Air bypass solenoid circuit poor electrical connection
- Air bypass solenoid leaking/blocked or stuck open/closed
- Air diverter valve leaking/blocked or stuck open/closed
Read more: http://engine-codes.com/p0410_gmc.html#ixzz2H3Wjt8f7

That is not an ABS system code, it is a powertrain fault code.P0411 - Secondary Air Injection System Incorrect Flow Detected, most common cause is a failed electric motor in the air injection pump.
The pump is under the hood.
Other Possible causes- Faulty Vacuum hoses damaged
- Air bypass solenoid harness is open or shorted
- Air bypass solenoid circuit poor electrical connection
- Air bypass solenoid leaking/blocked or stuck open/closed
- Air diverter valve leaking/blocked or stuck open/closed

P0410 - Secondary Air Injection System Malfunction
Possible causes- Faulty Vacuum hoses damaged
- Faulty Air Pump inoperative
- Air bypass solenoid harness is open or shorted
- Air bypass solenoid circuit poor electrical connection
- Air bypass solenoid leaking/blocked or stuck open/closed
- Air diverter valve leaking/blocked or stuck open/closed

This is likely a pump problem caused by water being sucked into the secondary air injection pump under the hood.

P0410 - Secondary Air Injection System Malfunction
Possible causes- Faulty Vacuum hoses damaged
- Faulty Air Pump inoperative
- Air bypass solenoid harness is open or shorted
- Air bypass solenoid circuit poor electrical connection
- Air bypass solenoid leaking/blocked or stuck open/closed
- Air diverter valve leaking/blocked or stuck open/closed

Read more: http://engine-codes.com/p0410.html#ixzz24VOZPAy2