Check engine light (p0400p) help

Cesarlcase · Aug 24, 2014

Hey guys, I have a relatively simple question. I just picked up a bone stock GSX. Check engine light is on and mech told me it was my o2 senser. Changed out the o2, but code was still there. Bought a cheap code reader and received code P0400 for egr, so I replaced it. Light was reset but 40 miles later it came back on. Now I scan it and I still have the same DTC p0400, but also in the pending slot, it shows it as pending as well. Why is it pending if it already has my egr as a DTC? Secondly, I replaced it with a new unit, any advice on getting things fixed? Thanks.

dragon181 · Aug 24, 2014

Try disconnecting the battery overnight to reset ECU.

jim95redgsx · Aug 24, 2014

Cesarlcase said:
Hey guys, I have a relatively simple question. I just picked up a bone stock GSX. Check engine light is on and mech told me it was my o2 senser. Changed out the o2, but code was still there. Bought a cheap code reader and received code P0400 for egr, so I replaced it. Light was reset but 40 miles later it came back on. Now I scan it and I still have the same DTC p0400, but also in the pending slot, it shows it as pending as well. Why is it pending if it already has my egr as a DTC? Secondly, I replaced it with a new unit, any advice on getting things fixed? Thanks.

The ECU does not check the actual EGR valve (on the intake manifold). It only checks the EGR solenoid (located on the firewall on the passenger side). Unplug the solenoid and measure the resistance of the solenoid. It should be between 36 and 44 ohms. If it's outside of this range, the ECU will post a PO400 DTC. Of course, it could also be a bad wire between the solenoid and the ECU. Make sure that the solenoid is plugged in.

Cesarlcase · Aug 25, 2014

jim95redgsx said:
The ECU does not check the actual EGR valve (on the intake manifold). It only checks the EGR solenoid (located on the firewall on the passenger side). Unplug the solenoid and measure the resistance of the solenoid. It should be between 36 and 44 ohms. If it's outside of this range, the ECU will post a PO400 DTC. Of course, it could also be a bad wire between the solenoid and the ECU. Make sure that the solenoid is plugged in.

Hey Jim, tthanks for the response. I actually pulled off the solenoid and noticed it was full of this "wax" so I cleaned it off best as i could and plugged it back in and received a new code for the solenoid. So my question is, since the code came on after I pulled the plug does that eliminate the possibility of a bad solenoid? I will test the ohms tomorrow after work. Thanks again.

jim95redgsx · Aug 25, 2014

If you unplug the solenoid with the key on, the ECU will throw out a new DTC code. This DTC will usually persist for three engine on/off drive cycles, even if the problem is fixed.'

That "wax" is probably dielectric grease. get a spray can of CRC contact cleaner. That should clean up the plug. With the key on and the plug plugged in, wiggle the wires going into the plug. See if the DTC comes back after it's cleared.

Cesarlcase · Aug 28, 2014

Yeah, the solenoid DTC went away but that damn p0400 hasn't. I'm hearing that it may be the ports on the intake manifold that are clogged. Can I clean that with the IM on the car? Any ideas?

MJBean420 · Aug 29, 2014

Seafoam! And maybe try pulling off the EGR valve and spraying that down too. The one on my truck got caked one time and would stick causing a similar problem.

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Check engine light (p0400p) help

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