P0418 driving us nuts
01-30-2013, 09:06 AM
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P0418 driving us nuts Yes, I've read the factory service manual and searched here. This one is baffling.
'99 SS M6. It's my dad's car (71 years old, the SS is his winter beater). Dad's pretty handy but when it comes to the computer stuff, I help out a bit.
He had let the exhaust system get so bad that the car had started to throw 02 sensor codes from the leaks, but it had other codes too. We finally installed a new exhaust system for him, which cleared all of the codes except for a P0418 (Secondary Air Injection).
I assumed the pump had taken on water, like many other GM's I've owned. After checking the fuses, I bought a new pump at Autozone. When I removed the old pump, it looked okay so I hooked it up to the battery. It ran. Huh. I returned the Autozone pump and put the old one back in.
If I jump across the relay, the pump runs. But it's not running when it's supposed to be commanded on by the PCM. After a whole lot of troubleshooting, dad determined that the circuit between the PCM and the air pump relay was open. He installed a jumper between the PCM and the relay. He said the pump was running with the key on, and sometimes with the key off. I knew this was wrong, so I went over yesterday to investigate.
He had hooked the air pump relay up to the MIL lamp wire at the PCM. In his defense, it is a brown wire just like the air pump, but it's on the opposite side of the connector. He now had all sorts of other codes related to the O2 sensors on both banks. This is good, though, because the pump was running when it shouldn't have been and the O2 sensors could "see" the difference. So the O2 sensors are functioning properly.
I jumped the circuit from the correct wire on the PCM to the air pump relay and cleared the codes. I don't hear it running, but the light stayed out for a couple of cool down and warm up cycles. This morning, however, we're back at square one. P0418 again, all the other codes are gone.
My dad insists that the problem is that the relay is loose in the fuse panel. I don't buy it. What are the chances that the PCM is bad? I know we can just tune it out, but dad would like it to function like it should.
To make matters worse, the car is due for emissions testing tomorrow. It will automatically fail with the SES light on. The State of NJ plugs into the OBDII port to check for codes, so I can't just clear it and run it through.
Anyone else run into this?
'99 SS M6. It's my dad's car (71 years old, the SS is his winter beater). Dad's pretty handy but when it comes to the computer stuff, I help out a bit.
He had let the exhaust system get so bad that the car had started to throw 02 sensor codes from the leaks, but it had other codes too. We finally installed a new exhaust system for him, which cleared all of the codes except for a P0418 (Secondary Air Injection).
I assumed the pump had taken on water, like many other GM's I've owned. After checking the fuses, I bought a new pump at Autozone. When I removed the old pump, it looked okay so I hooked it up to the battery. It ran. Huh. I returned the Autozone pump and put the old one back in.
If I jump across the relay, the pump runs. But it's not running when it's supposed to be commanded on by the PCM. After a whole lot of troubleshooting, dad determined that the circuit between the PCM and the air pump relay was open. He installed a jumper between the PCM and the relay. He said the pump was running with the key on, and sometimes with the key off. I knew this was wrong, so I went over yesterday to investigate.
He had hooked the air pump relay up to the MIL lamp wire at the PCM. In his defense, it is a brown wire just like the air pump, but it's on the opposite side of the connector. He now had all sorts of other codes related to the O2 sensors on both banks. This is good, though, because the pump was running when it shouldn't have been and the O2 sensors could "see" the difference. So the O2 sensors are functioning properly.
I jumped the circuit from the correct wire on the PCM to the air pump relay and cleared the codes. I don't hear it running, but the light stayed out for a couple of cool down and warm up cycles. This morning, however, we're back at square one. P0418 again, all the other codes are gone.
My dad insists that the problem is that the relay is loose in the fuse panel. I don't buy it. What are the chances that the PCM is bad? I know we can just tune it out, but dad would like it to function like it should.
To make matters worse, the car is due for emissions testing tomorrow. It will automatically fail with the SES light on. The State of NJ plugs into the OBDII port to check for codes, so I can't just clear it and run it through.
Anyone else run into this?
01-30-2013, 09:41 AM
#2
TECH Apprentice
http://www.ls2.com/boggs/dtcs/DTC%20...s/image003.gif
http://www.ls2.com/boggs/dtcs/DTC%20P0418.htm
true this is for a ls2 but i suppose its the same.
check your Air bypass solenoid harness if open or shorted, Air bypass solenoid circuit electrical connection
http://www.ls2.com/boggs/dtcs/DTC%20P0418.htm
true this is for a ls2 but i suppose its the same.
check your Air bypass solenoid harness if open or shorted, Air bypass solenoid circuit electrical connection
01-31-2013, 04:56 AM
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Okay - pulled the codes and the only one there now is a P0410, which says that the O2 sensors are not seeing the necessary change in oxygen levels when the pump runs.
This could either be the pump not running or the solenoid, I think.
My dad verified last night that the correct wire from the PCM is indeed open between the PCM and the air pump relay. So, that means the jumper I installed should work. He's sticking by his relay-is-too-loose theory and jammed a little bit of wire in there to make sure it seats tightly and there's a good connection.
This could either be the pump not running or the solenoid, I think.
My dad verified last night that the correct wire from the PCM is indeed open between the PCM and the air pump relay. So, that means the jumper I installed should work. He's sticking by his relay-is-too-loose theory and jammed a little bit of wire in there to make sure it seats tightly and there's a good connection.
