Check gauge light flickering

[Tbruz]

1997 Tahoe 5.7L with 137K miles
At first start in morning I'm getting a flickering "check gauges" light on dash.
Initial start is ok(NO LIGHT) but as soon as I drop it into gear, the light flickers and glows, If I add RPMS, light goes out.

Any other starts in the day are fine, no check gauge light


Water Temp is stone cold as truck has been off for 12 hours and overnight temps in NH are still low to mid 30's
Oil level is full and newly changed with 5 30W
Oil pressure at start goes to just under 60lbs
Oil pressure comes down when warm and or at idle to under 40
Amps show a hair over 14
RPMs around 600
No codes stored check with a cheap OBDWiz scanner

Any ideas?
Thanks
Tbruz

 

[SunlitComet]

you should be fine on your measurements. it is possible the check gauge driver circuit has issues. but the way you describe it sound like it is responding to oil pressure. the oil pressure gauge moves slowly so it may not hurt to stick a oil pressure test gauge on the engine to verify the pressure and pump functions. if it is fine you might want to try replacing the sender in case it has intermittent issues that the dash meter can not respond to fast enough. I have not seen the light circuit act up before because of the chip driving it so far.

 

[Tbruz]

Thanks for your input.
Just ordered sending unit acdelco 19244500, will replace it over the weekend and post back.
Looks like its in a tough place to reach and the dizzy may have to come out to actually get to the sender.
Tbruz

 

[SunlitComet]

you might try getting the vehicle high in the air and try reaching it from above the left y-pipe.

 

[Tbruz]

Installed new sender and no more flickering check gauge light.
Needed to go from the top down while laying on my engine, dizzy stayed in place, but I did have to borrow the "oil-pressure-sending-gauge-socket" from a bud.
Thanks
Tbruz

 

[Tbruz]

First start this morning and Check Gauge light came back on for around 45 to 60 seconds.
Sender did not fix the issue.
I have a spare instrument cluster and I have installed it for tomorrow mornings cold start. Trying to rule out the in-cab electronics as a possible cause.

Any other ideas are welcomed.
Thanks
Tony

 

[Tbruz]

So the spare dash cluster I had shows the same issue, Check Gauges light comes on at first start only; stays on for approximalty 60 seconds, flickers even if I am driving and goes out; never to be seen again until next days first start.

New oil sender
fresh oil change and filter(albeit a quick change shop oil filter)
No high temp readings(cold start)
Amps at 14ish
oil pressure over 60 at cold start
ruledout dash cluster using a spare.

Where do I look next???
Thanks
Tbruz

 

[SunlitComet]

well by process of elimination that would leave a wiring issue left, an actual oil pressure issue(as strange as it sounds) or a temp sender issue. in any case the last two items should likely show up as issues when looking at the gauges.

 

[Tbruz]

So over the weekend, Fri, Sat and Sun I tried two different spare clusters, with same results on both(all three if you count my real cluster), check gauge light comes on at first start, no top end noise and its off in 60 seconds, never to be seen again until next days first start.
By the way the OP gauge on both spares and on my real cluster read roughly the same and react similarly, 60 at cold start and drops when warm, never below 20 PSI
I also tried replacing the temp sender on the DS head and at the thermostat housing having already had the new OP sender replaced I'm certain its not the senders or gauges themselves.

Getting my hands on a mech OP test gauge to check the pump pressure at the filter bung.
Will report back on that.

Could a cheapo (bad internally collapsed) filter be causing this??


Not thinking wires Sunlit, as it never comes back after the first start...........
Thanks
Tbruz

 

[SunlitComet]

filter is upstream of the sensor so if filter got clogged for example it would be bypassed and continue to move oil which the sensor would see.
spock once said "Once you have eliminated the impossible, whatever remains, however improbable, must be the truth." there is no system or circuit in the whole vehicle that can make it act like that for a reason. it does sound like possibly engine compartment heat might be contributing as well but one step at a time.
try the filter for the hell of it and if that does not work you may have no choice to look at a wire issue as far fetched it might seem.

 

[Tbruz]

A mechanical gauage was isntalled on the manifold( in place of the OP sending unit) ; reads 47 lbs at first start, around 1000 RPM.
Mech gauage responds similarly to dash gauge, i.e higher pressure with higher revs, lower pressure at idle or warm.
Based on this test I beleive the Oil Pump is fine and the gauge is reading correctly.
Changed out Oil filter to a WIX and changed oil again ensuring its quality 5w/30w and at the correct level.

Same thing happening, cold start, no light for 1 second at initial start.
then 1 to 2 seconds after started the check gauge light comes on for around 60 seconds.
New data point is that if truck is left to get stone cold (say 12 hours later) same thing happens, No light for 1 to 2 seconds followed by up to 60 seconds of Check Gauge light.

Dash itself, OP sender and 2 Temp senders already ruled out in earlier tests.

Where to next ??
Grounds? If so where are they.
Individual wires? which ones
PCM?

Thanks for any input
Tbruz

 

[SunlitComet]

there are two ground wires you can check for resistance. remove the cluster and pull the connector from dash slightly. black/white and black measure the resistance all the way to the battery looking for anything unusual along the entire path and you can narrow further from there. other then that that and assuming you have a good 13+volts on your gauge, showing that good voltage is reaching the cluster on the two pink wires from separate fuses(one really does not have a role in this light at all btw), that leaves me a bit stumped at the moment.

 

[Tbruz]

Problem Solved and verified at this mornings 1st start; no more Check Gauges light.

Vehicle was brought to my mechanic who re-validated that all senders, oil level,oil quality, mech reading of Oil Pressure were in fact correct. On the recommendation to check wiring, the ignition switch wiring was pursued. They measured a voltage difference in a wire pre-start, post start(under 60 seconds) and post start(over 60 seconds)
R&R'd ignition switch harness and Problem is solved!
Thanks
Tbruz

 

[SunlitComet]

which wire please?

 

[Tbruz]

I wasn't there but I'll try to get specific wire details.

Per the mechanic, it was the feed side of the transmission fuse in the interior fuse block.

I do know they had hooked up their remote start controls and noted that when they remote started the vehicle there was no CG light versus a start with key in; CG light on for around 60 seconds.
Tbruz