ECM not engaging Crank Relay and Fuel Pump Relay

[Esstover]

Background….

car started and runs. I took it for the first short trip to the gas station and it was getting hot. I didn’t properly refill the coolant system after having to pull the powertrain for a clutch issue. So I pulled the car in the garage and it was hot. I guess I’ll have to admit that I opened the coolant reservoir tank. It was empty… but not really. So I ended up with steam and hot coolant everywhere. So after a bit I rolled the car out of the garage to spray it off a bit. Now when I turn the key on everything powers on (lights, fan for the SC coolant loop, dash) but I don’t hear the fuel pump and it won’t crank. I checked fuses and relays. I can jump where the Crank relay goes and the start cranks. I can jump where the fuel pump relay goes and it runs. I pulled the clutch sensor and checked it. It’s working fine. So for some reason I think the ECM is not commanding the fuel relay and/or crank relay. I checked my grounds and they seems good. I have a cheap OBDII and all I get is a code about the TC bypass solenoid (note I have a SC car).

One question… should the Pink/White wire ring out to ground when they key switch is in the off position? I get 12V when it’s on, just wasn’t sure if it going to ground when the switch was off made sense.

I also put the battery on charge over night to make sure it wasn’t a low battery issue.

What do I check next? Is it possible somehow the steam got moisture in the ECM and damaged it?

 

[Joebob]

From my understanding NO pink or Pink/White wire should ever be grounded to the chassis. These are +12V sources and will blow fuses or relays if grounded.

Joe

 

[Rauq]

I have a cheap OBDII and all I get is a code about the TC bypass solenoid (note I have a SC car).

What exactly is the code?

One question… should the Pink/White wire ring out to ground when they key switch is in the off position? I get 12V when it’s on, just wasn’t sure if it going to ground when the switch was off made sense.

As previously stated, can't think of any pink wire that should be grounded. Which wire are you talking about?

Does the throttle body move or make any noise when you switch the key to the on position (not start)? This will tell us if it's not starting because the computer doesn't want it to, or because of some other issue.

 

[Ross]

What are the OBDii codes?

Red wires on a Cobalt are typically "battery positive voltage" wires, then once they go thru a fuse, are
Red wires with a White stripe. If they also go thru the run/start relay, then they are typically
Pink wires, that are switched by the key.

I'm not sure about pink with a white stripe.

 

[Gtstorey]

Hot wire will sometime "tone out" to ground through a load, whether that's through a light bulb, or maybe through the coil side of a relay.

 

[Esstover]

Thank you all for the quick responses.

so I’m in the agreement with @Gtstorey and I’m just ringing them to ground. If I actually try to read 12v by using one of the wires as ground that doesn’t work. So I don’t think that is the issue.

I spoke a little from memory on the wire colors. @Ross is correct. A pink wire is what I was dealing with at the clutch switch which would be after the key switch.

As far as the actually code i’m a little handicapped. My brother in law was here with his dongle last night but I don’t have it now for the code number. I just know it was something about a TC bypass Solenoid. I called and he’s going to run back over in an hour or so and I will get the code. I’m going to guess based on my search it was P00333, but I will confirm and get back with


when I turn the key I do get movement on the throttle body.

 

[Gtstorey]

You have to be careful with some of the descriptions provided for codes and especially in some of the cheaper readers. Often they will be a generic description and may be close but they really need to be confirmed in the service manual. At the very least an internet search needs to be ran withe the code number and "Cobalt" and if that doesn't give any results, GM. And a lot of the codes are sort of interchangeable between SC and TC although the service manual will differentiate. But I don't think the P0033 will cause a no start but will limit the boost, but I'm not sure about that without checking the manual.

And you typical trouble codes will be 1 letter and four numbers.

HPT tuners has some of it's tables still labeled SC for the TC model also.p033

 

[Esstover]

got the reader back. It is p0033. From what I’ve read this shouldn’t be keeping me from starting

 

[Gtstorey]

My first guess for the no start is going the be a loose connection or bad ground. You probably moved something while cleaning up or just have enough moisture in a loose connection to cause a problem. Try wiggling wires around the fuse box to see if that causes any clicking or allows it to start. At some point you may to determine if this is a no spark or no injector that is keeping it from starting.

 

[Esstover]

My first guess for the no start is going the be a loose connection or bad ground. You probably moved something while cleaning up or just have enough moisture in a loose connection to cause a problem. Try wiggling wires around the fuse box to see if that causes any clicking or allows it to start. At some point you may to determine if this is a no spark or no injector that is keeping it from starting.

So I had read if I turn the key to the run position and jumper the crank relay socket it will start. It cranked but didnt start because the fuel pump wasn’t running. I jumped the fuel pump relay socket and the fuel pump ran. When I then jumped the crank relay socket it started and ran out the gas I had pumped in. So those are all good things. Starter is good, fuel pump is good, engines not hydro locked. So why is my fuel pump not coming on? And would it not crank if it doesn’t see fuel pressure? I guess I’m thinking if I figure out the fuel pump it might fix it.

 

[Gtstorey]

It will crank without fuel pressure. (at least on most vehicles)

 

[Esstover]

Bump

still broke. Made a 4 hour round trip today to get a new fuse box. Still same problem. I really don’t think it could be the PCM but I guess. What I don’t get is the tiny noise I hear when I release the key that sounds like a little arc. I dunno. I’m going to focus on the ground connections again tomorrow. Any other thoughts??

 

[Ross]

Background….
car started and runs. ... when I turn the key on everything powers on ... but I don’t hear the fuel pump and it won’t crank. I checked fuses and relays. I can jump where the Crank relay goes and the start cranks. I can jump where the fuel pump relay goes and it runs. ...

Since the fuel pump runs when the relay is jumped, I wonder if the PCM isn't giving power on the dark green wire with white stripe, which connects via Fuse block via C2 connector, wire f6.
Or if the fuel pump relay isn't getting ground on connector C3, wire f2. You could electrically test at the fuel pump relay.

The start relay gets power from the BCM IP Ignition 10A fuse, then goes thru the clutch start switch then to Fuse block via C2 connector, wire c1.
The start relay gets ground from the Fuse block via C2 connector, wire d1, then to the PCM, which will have some logic to determine if it wants to start the engine.

Found "Starting and Charging Diagrams" here on AllDataDIY.

Both of these issues use the Fuse block C2 connector. I would want to loosen that bolt, push on the bolt to slide the connectors off, then retighten the bolt to draw the connectors back on. Reseating that connector may fix these 2 issues. Just a guess... it could also be the PCM having data issues on the GM high speed LAN, and not getting the information it needs to allow an engine start.

I would be tempted to jump the fuel pump relay, and momentarily jump the starter relay, and do some test drives... see if you get any more issues or symptoms that might guide us as to what the issues are. I ran a low amperage purple wire to my starter, thru the rear firewall, into the cabin, so I could jump my starter motor by providing 12V+ to that wire, via the aux. power port (cigarette lighter) I have in my cabin. Ran that way for about 6 months until I could figure out what was my GM LAN issue. The purple wire allowed me to start the engine quickly, as occasionally I stalled the engine in traffic. The car still needed the key for the engine to start, so I wasn't overly worried about someone stealing my goblin.

 

[Esstover]

Since the fuel pump runs when the relay is jumped, I wonder if the PCM isn't giving power on the dark green wire with white stripe, which connects via Fuse block via C2 connector, wire f6.
Or if the fuel pump relay isn't getting ground on connector C3, wire f2. You could electrically test at the fuel pump relay.

View attachment 41996

The start relay gets power from the BCM IP Ignition 10A fuse, then goes thru the clutch start switch then to Fuse block via C2 connector, wire c1.
The start relay gets ground from the Fuse block via C2 connector, wire d1, then to the PCM, which will have some logic to determine if it wants to start the engine.

View attachment 41997

Both of these issues use the Fuse block C2 connector. I would want to loosen that bolt, push on the bolt to slide the connectors off, then retighten the bolt to draw the connectors back on. Reseating that connector may fix these 2 issues. Just a guess... it could also be the PCM having data issues on the GM high speed LAN, and not getting the information it needs to allow an engine start.

View attachment 42001
I would be tempted to jump the fuel pump relay, and momentarily jump the starter relay, and do some test drives... see if you get any more issues or symptoms that might guide us as to what the issues are. I ran a low amperage purple wire to my starter, thru the rear firewall, into the cabin, so I could jump my starter motor by providing 12V+ to that wire, via the aux. power port (cigarette lighter) I have in my cabin. Ran that way for about 6 months until I could figure out what was my GM LAN issue. The purple wire allowed me to start the engine quickly, as occasionally I stalled the engine in traffic. The car still needed the key for the engine to start, so I wasn't overly worried about someone stealing my goblin.

My 'first start' toubleshooting ended with me tightening the 7mm bolts on the fuse box. This issue seems very similar but I have had the top off the fuse box off several times and even the new fuse box top. I always tighten them as much as i can. I'm not sure what else to do to make sure I am making connection. I pulled some connectors today and used the multimeter to make sure they went pin to pin. I checked the dark green with white stripe between the PCM connector and C1 at the fuse block and i checked the yellow coming from the clutch switch. I also checked grounds. Then I checked the GMLAN wires that go from the PCM plug to the BCM plug. Then I started looking at the old PCB I took out of my original fuse box. It has some corrosion and black where the Run/Crank relay connects. One of the PIN's (C1 Underhood F3) is for a ground and I chased that goes to the A/C compressor plug which I had unhooked. so I thought maybe I had found something. I snipped the plug off and ran it to ground. That didn't seem to change anything. That seems a little odd to me that the PIN which appears to be the ground side of the coil of the Run/Crank Relay wen to that plug. I need to find that in the diagram and sort it out in my head.

How do I determine if the PCM is screwed up? As mentioned before I just had a bluetooth OBDII reader and a free app. If I go borrow a reader from Autozone will I get more info? or do a need a more advanced reader? or HPTuners?

 

[Gtstorey]

The best scanner for troubleshooting these are a tech2 or clone. The next is a somewhat higher end scanner like Topdon Phoenix or Higher end Autel. You might get enough data from HPT but it won’t get all of the body control or theft deterrent module problems.

Just because the nuts are tight on the back of the fuse box doesn’t mean the individual wires are making a good connection.

 

[Esstover]

Worked on in some troubleshooting with @Ross this evening. Turns out my fuel pump relay is functioning properly. It’s just quiet and the PCM doesn’t call for it if there is already fuel pressure. I jump the Crank relay and it runs, but not with the MAF unplugged.

@Ross asked me to post pics of my leftover connectors to make sure I haven’t left something out.

struggling a little doing this on my phone. I believe I have a washer fluid level, fan plug (with the white wire from the fan plug I cut), a/c connector (think it’s the one I cut), the evap plug, and I’m not sure what the round one is.



View attachment 42044

 

[Esstover]

Sorry for the late update. Problem is resolved.

Apparently one of my ground wires in my harness lost connection. It was the one running to the C1 plug for the PCM. When the PCM was trying to complete the circuit for the Crank relay coil it wasn't going to ground.

Thanks for all the help.

 

[Gtstorey]

I guess that puts bad ground up to 62% of the time.

 

[Robinjo]

I guess that puts bad ground up to 62% of the time.

It's always a ground. Step 1.... triple check your grounds.

Glad your issue got resolved though.

 

[G Atsma]

It's always a ground. Step 1.... triple check your grounds.

Glad your issue got resolved though.

That's likely the biggest thing I harp on over at my other hangout, LS1tech. And more often than not grounds are the issue. It can't be stressed enough. Check EACH one. Wiggle, yank (gently...), eyeball intensely, just make sure they're good!
OK, stumbling off the soapbox now.....