07 LBZ Fuel Pump Relay

[swinters]

I've been trying to figure out whether I need to change out all 7 of the same style relays in my fuse box but can't find any info on why GM has changed the part number - twice. Even the dealer hasn't been able to help. Does anyone here know anything about these relays? I don't want to blindly throw parts at the truck. Here's a cut and paste of the post I made this morning on the Duramax Diesel site (no replies):


Several years ago a Chevy dealer identified the Fuel Pump Relay in the underhood fuse/relay box as the cause of repeated P0090 codes on my '07 LBZ. After they finished with it the truck ran for a long time without setting that code again (I did get some other codes but it turned out to be the clips on the back of an engine harness plug). About a year ago it set the P0090 code again so I swapped the fuel pump relay and one of the others (my truck has 7 relays with the same part number), cleared the code and it has been fine until two days ago. Same thing with the P0090 and limp mode, swapped in a different relay (DRL this time), cleared the code and am back in business. Looking at the schematic it appears that this relay, even though there's no factory fuel pump, provides power to the ECM and fuel pressure monitoring. When the relay is open and the engine is running the truck sets a P0090 and goes into limp mode. The first symptom is injector knock when the truck starts and then I get the P0090.

It seems to happen on hot days and day before yesterday it was over 90F, so I decided to see whether they sold a heavy duty version of the relay. The first thing I did was go to a GM parts site and enter my VIN, and then the part number for the 7 relays the factory put in my truck (15328866). The site returned that this part did not fit my truck. I looked at the details and it said that this part was replaced by 19115080, so I ran that against my VIN and it said that part didn't fit my truck either, but then looking at the details it said that relay was replaced by 19116057 so I ran that and it said that relay DOES fit my truck and identifies it for several application, including the fuel pump relay.

I've been trying to find the specs for the different relays and the only thing I've found is that the 19116057 relay carries the AC Delco part number D1786C. No breakdown that shows anything like contact material or coatings, amperage ratings, etc. What I'm wondering is whether the original relays, Part No. 15328866, are defective or inadequate for the load they're carrying and whether I need to change out all 7.

Does anyone have any insight on this issue or know where I could find the info?

 

[WarWagon]

Fuel Pressure Regulator issues. Start with wiring if I recall correctly there is a area by the alternator that can rub through. (We burned the harness badly on our LMM where it by and touched a boost tube on the driver's side.) Quit focusing on just the relay unless you test it and several come out bad. Check every single fuse including condition of the contacts. Then trace all of the wiring harness for rub through and shorting out. I suggest a wiggle test seeing if the scanner pops a code. Dare I say grounds and condition of battery connections? Both batteries load test good? Last: Ignitions switches were not reliable in this era. Nevermind the low torque deaths: they simply burnt contacts up.

 

[Will L.]

Double check what WarWagon is telling you.

Change out all 7 relays? Usually when a relay can not carry it's load, it will fail under testing and you could replace just the known unit. If the relay is underbuilt and is the fault then updating to the new relay is the answer, but usually the wiring is sized along with the relay to the concept load. So if relay is frying, and you go to a heavier relay, itnis like replacing a 10 amp fuse with a 20 amp fuse and eventually the wires fry.

Having this as an answer from a dealership but they cant get the full answer does not sound right. Normally they have all the info in the same bulletin. Gat your hands on that bulletin, or the multiple bulletins related- dont go by "Jack says to...".

On the AC Delco part question, have you called technical support at AC Delco? I have called them a few times over the years. It sometimes takes a few days of phone tag to get the right person, but they were good at getting me in touch with the right person. With email more prefered by most every company now, that might be a better contact method. Do your best to get the bulletin before contacting them.

 

[swinters]

Thanks for the ideas! It's been a couple of years since I went over the wires and looked for rubs and checked the grounds so it wouldn't hurt to do that again for sure. I have a Tech2 and set of factory manuals and have run every scan in the book and everything is within limits and no codes, plus have done the resistance checks of the FPR and other components. Looking at the schematic it looks like the only thing that could draw excess current and mess up the relay would be a short so I've gone crazy trying to find it. It never occurred to me that the relay might not be up to par but now that I see that GM has changed the part number - twice - I'm beginning to wonder whether the problem has been junk relays all along. The problem with that idea is that when I swap the relay to another component that uses the same relay, like the Daytime Running Lights, it works fine. I probably need to sit down with the schematics again and see what I'm overlooking on what the load is on that relay. In the meantime, the new relays are less than $10 plus $2 shipping, so I've ordered a couple and will check them out. I sure would like to find the specs. on the relays, or at least something on why the part numbers have changed though.

 

[THEFERMANATOR]

Which relay exactly are you refferring to because unless you have a cab and chassis truck, there should be no relay in the fuel pump spot. I'm not the most familiar with lbz wiri,g, but I know on earlier trucks the fca was powered off of a 10 amp fuse and a keyed on power source. You have 2 wires to the fca, a power wire, and a negative that the ecm pulses to control fca current to regulate flow to the cp3 and control pressure. Lbz's don't have any real known wiring issues like lb7's and lly's had, but it's normally a good idea to start by checking the pins in the bale plugs. It's not uncommon for a pin to not be seated all the way, and lose contact over time. Next time you're having issues, unplug the fca(regulator), and see if you have battery voltage on I believe it was a yellow and red wire.

 

[swinters]

The pins were a problem on my truck too! Actually the TPA's on the engine harness Delphi plugs (the clips on the back side of the plugs that hold pressure on the backs of the pins so that they don't back out of the plugs). I was getting all kinds of random codes for cam sensor and stuff like that and they'd come and go. After the last dealer worked on the truck and identified the fuel pump relay as the problem everything worked fantastic until about this time last year when I was up in the middle of the Yukon and it started doing to multiple random codes again. I pulled into a gravel pit and started going over the wiring and found that one of the TPA's wasn't latching on one side and the other one on the same plug was missing. I walked around looking for something to jam behind the locking leg to keep it latched and found a piece of cable TV coax, cut the length I needed, unplugged the plug and worked the TPA back in place and stuck the wire in to hold the latch in place. Fired it up, cleared the codes and drove the rest of the way to Anchorage and back to WA State, then hooked up my 5th wheel and drove to Missouri, all over Utah, and then back to WA State with that roadside fix in place and never another problem. I've since replaced the TPA's (about $2.50 each) and no more codes.

I thought the same thing about the relay being there only for the cab & chassis but the mechanic at the dealer said that it powered the circuit that measured rail pressure (if I remember right). After having it act up again the other day after it had been working so well for so long I've just started digging back into it and came across the change in relay part numbers and wondered whether GM changed them because there was a problem with the original ones.

I've always said that diagnostics was like detective work and is all about gathering evidence. You keep digging and you'll find the culprit. I don't drive the GMC much (only has 60K on it) so I probably haven't dedicated the time to it that I should.