Code P304 and P1404 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 04-15-2010, 02:47 PM   #1
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Default Code P304 and P1404

My CEL came back again a few weeks ago. Just had a chance to pull the codes again. Same cylinder as last fall. I had swapped the coils back then, and it worked fine all winter, but it didn't get any highway time. Took it on the interstate and mashed the throttle (of course) and started spitting and sputtering. The CEL flashed a few times then stayed on. The code is for the same cylinder as before swapping the coils, so it'* not that. I think I'm just going to get a new set of wires and a new injector for that cylinder, the plug was new, but could've gone bad already I suppose. Inj 3 was bad when I bought it a few years ago, so it'* quite possible this one is going bad too. Anyone have luck with mechanic in a can for this, ie JB or 3M Fuel injector cleaner? I think it'* been 30k since I last ran a bottle through.

I'm assuming the 1404 EGR valve code is due to the misfire, or should I be looking at it the other way around? The EGR problem is causing the misfire. In the past, I didn't always get an EGR code when I got the misfire.

This is for the 99 ssei btw.

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Old 04-15-2010, 03:15 PM   #2
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I would check for a cracked EGR tube. A leaking tube could also cause a misfire, but I would expect a p0300 for that. Changing the wires is a good idea and may correct the misfire.
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Old 04-16-2010, 05:43 PM   #3
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Document ID# 367907
1999 Pontiac Bonneville

DTC P1404 Exhaust Gas Recirculation (EGR) Closed Position Performance









Check for the following condition(*):
  • Check for excessive deposits on the EGR valve pintle or seat. Remove the EGR valve and check for deposits that may interfere with the EGR valve pintle extending completely or cause the pintle to stick.
  • Check for poor connections at PCM or EGR valve. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor temrinal to wire connection.
  • Check for a damaged harness. Inspect the wiring harness for damage. If the wiring appears to be OK, connect J 39200 DMM and check circuit continuity while moving connectors and wiring harnesses related to the EGR valve. A change in the DMM display will indicate the location of the malfunction.
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Old 04-16-2010, 08:55 PM   #4
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Of course, a misfire may blow carbon back into the egr valve pintle

and hold it open. Those linear valves were problematic.
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Old 04-28-2010, 12:53 AM   #5
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A new set of wires did the trick. Thanks for the tips. I didn't dig into the EGR for fear of what I might find. It'* running great now.
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Old 04-28-2010, 06:29 AM   #6
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You may find a slightly rough idle at times but generally running fine.
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