2000 suburban ground issues

[bufmatmuslepants]

I bought a 2000 suburban LT with 239k miles for $1800, extremely clean. It had a check engine light with P0332 knock sensor bank 2 low input and P0430 bank 2 catalyst system below efficiency. It also would throw LOW OIL LEVEL and LOW WASHER FLUID lights after running for a bit, and sometimes the ABS and BRAKE lights. As soon as I would shut it off then restart it, all lights go away except check engine, so I knew it was a ground issue. The engine doesn't smoke or knock, good oil pressure, oil level is fine, washer fluid level is fine.

I started with grounds, I cleaned the battery terminal ground, and for the first 10-20 minutes it would only have the check engine light, but after it got warm it would still throw the ABS and BRAKE lights. I cleaned the EBCM ground, no change. It was idling at 550rpm normally, but after disconnecting the negative battery terminal for 15 minutes while I cleaned the ground it would sputter down to 100-200rpm and took a bit for the IAC to catch up, so I cleaned the TB and it is a little better.

I put my timing light on the plugs on bank 2 and was not getting consistent spark from the passenger side second one back, so I changed the plug to a NGK platinum gapped a touch tighter at 0.055. Still not a good spark from the timing light. Then I unplugged each coil and every coil did change idle so all are firing, timing light must not be able to pick it up well.

I put a meter from battery to frame and battery to the alternator bracket where it says GND and with the engine off I got 0.3 ohms, so good, but engine on and warm I got 60-70 ohms. I cleaned the battery to block ground and the battery to frame ground and now it's 25 ohms engine on, can someone verify this is ok, or measure on their car? I feel like that is high. I moved the battery to block ground a little farther away from the block so it doesn't get as hot. I cleaned the block to firewall ground at the firewall and couldn't reach the other end at the back of the block in the dark, but still negative battery to firewall is 25 ohms running.

I ran 10 gallons of shell 93 with Lucas fuel injector cleaner the day I bought it, and now it has a full tank of Sheetz 87 with another bottle of Lucas fuel injector cleaner.

Today it made it 35 miles and 45 minutes to work without throwing any lights at all, but I don't think I am out of the woods yet. I am now leaning towards spraying brake cleaner on the intake to find a leak, and possibly replacing the intake gasket, I don't think the knock sensor is bad since the bank 2 catalyst code tells me that bank does have an issue. I have not spent a lot of time with LS engines and while it is smoother than my old tbi 350, vortec 350, or LT1, I think it should idle smoother. Other options are clean the MAF, replace the rest of the plugs and put on new wires, and buy a brand new battery negative cable. The plugs on it are AC Delco platinum with normal wear, and the wires look decent, I have all new plugs but haven't bought new wires yet.

Any ideas?
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[bufmatmuslepants]

It has a bunch of other little issues like the rear lift gate won't lock and the window won't unlock, only 1 speaker works, power mirror switch won't work, a few knobs missing from the head unit, memory seat button doesn't work, driver seat is torn, but other than that it runs and drives great, I already did front rotors as they were not cut when new pads were installed. I am thinking of flipping it for $4000, or keeping it through holiday family travel.

[bufmatmuslepants]

Sorry I am posting this from another thread I created on LS1tech, explains the past tense and present.

ABS and brake lights came back on on my way back from lunch, but cleared when I turned the motor off then on again.

Then on the way home the SES light came back. Then a few minutes later something changed, the idle went high, like 750 in gear and 1050 in park, I don't know if the fuel injector cleaner worked something loose, or I hit a sweet dead spot in the coolant temp sensor causing it to go into high idle, but when I got home I turned it off, cycled the key 3 times to reset the IAC, and it fired back up as normal.

Changed the oil, got just a touch over 5 quarts out of it, just enough to hit the top of the new 5 quart jug, even though the dipstick said full. It was for my peace of mind knowing 6 quarts was in there and the low oil light is not actually because of low oil. The FRAM filter I pulled off was way heavier than it should have been even though the PO said he changed the oil 500 miles ago, the oil was dark but not too bad, a little sludge on the plug but not awful. I put in Castrol GTX high mileage advance auto special with a purolator filter, will change it again after 1000 miles just to clean any sludge it works loose. Oil pressure looks better, it used to always be at 20psi at idle even when cold, now it's 30-40, I was concerned sludge had filled the oil filter and was somehow causing the low oil light.

Changed the rest of the plugs and wires, the Carquest premium wires were shorter than the ones I took off, no slack but they fit.

Cleaned the MAF with MAF cleaning spray, it was pretty dirty. Disconnected the battery while I did this to clear the PCM.

Fired it up, it stalled out the first few times until I feathered the throttle and it let the IAC catch up. It still only idled around 500-550rpm, is this normal? It is smoother now, but I feel like it should be higher, it's always at 550, in both park and drive. I might need to clean the TB more and the throttle position switch and IAC.

What causes it to go into high idle? Does the MAF reading cold IAT have anything to do with it or just coolant temp? I've never seen it go into high idle, even in the morning, or kicking on the AC, it just has always stayed at 550ish. I think I need to ohm out my coolant temp sensor.

Only took it around the block but it feels better, smoother, even the trans shifts felt smoother. Took the bike to work today but I need to drive it a bit and see if the fixed it or if I still need to change the battery to frame ground. I have half a can of seafoam that I want to put through the brake booster to clean any carbon out as well.

Can anyone please do me a favor and measure your ground resistance when it's warm and running from the negative post to frame and negative to block? Is 25ohms normal? I had 70 when at operating temp before, what's the threshold for "problem"?

[PAWS 72]

My 02 truck isles at 500 rpm also. I thought it was because of the knock sensors being bad. My oil pressure is around 50 - 60 psi running somewhere 55 mph.40 idling. As far as grounding situation I dont know.

Hope this helps. Good looking Burb.

[truckdude239]

Okay so these trucks have issuses with the knock sensors you problay will need to repalce them and get the updated harness for them, check your ground on the back of the cylinder heads they have been know to cause issues

[WigglesTheHoly]

Interested to see where this goes, my 05 has an intermittent knock code abs light ( with abs actually engaging sometimes when it shouldn't) Then I'll hop back in and everything will be fine for another 500 miles rinse repeat. I checked grounds as well didn't find much.

[bufmatmuslepants]

thanks for the replys, about to do a 100 mile drive and see if any lights come on.
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[68C15]

Test alternator for any AC voltage at battery. You could have a bad alt causing back feed on th DC reading high resistance.

Your ABS will take a shop to scope the sensors and see if one or more sensors is having issues

Idle afte ECM reset could be a number of things. Again, a shop wit a scanner will be money well spent. Vacuum leak generally causes high idle if the ECM is at its limits. Do you have throttle cable or dive by wire? I'd spray carb clean around base of intake and see if idle changes. The gaskets are a known problem. While you have the intake off you can then replace the knock sensors and harness as well as make a dam of silicone around them. Water runs in there and corrodes the sensors/connectors.

The P0430 is most likely a bad converter. Aftermarket a work for a while. I've seen them last as much as 2 years. Again, a scanner with PID graphing will help so you can see the actual wave form. I have seen it throw that code when the front sensor is lazy and closely resembles the rear

None of your issues surprise me. They are all typical.

[bufmatmuslepants]

I drove the truck and the check engine light came back. Then coming home as soon as I started it the check oil level light came on. It has 6 quarts. The washer fluid light has never come back since I added water, so now I'm thinking that after 15 years and 240k it really is s bunch of bad sensors. The low oil might be a bad low oil sensor, it clears when the truck is restarted. The abs and brake light came back halfway to work today but clear as soon as the truck is restarted. I am thinking the knock sensor is bad, causing it to pull timing on bank 2, causing it to not get full complete combustion, causing the O2 sensor to read high oxygen, tripping that code. I highly doubt the cat is bad, almost every car or every friends car I've worked on, when you get that light and someone changes the cat it turns out to always be a bad O2 sensor, so I think it could be the sensor if anything.

I was changing out the blown speakers and had changed the rear speaker, turned the key on to test it, it worked, then as I was buttoning it up with the radio still on everything went dead. I had fixed the rear hatch lock and done the speakers with the dome lights on for about 20 minutes and then had the radio on for about 2 minutes and the battery was dead. I grabbed the Camaro battery and swapped it and it started no issue. Then put the battery in the Camaro and it was dead, so I charged it and left the Camaro battery in the truck.

Then I remembered my boss said what about a short from positive to ground, and I disconnected the battery and key off, I got no short positive to ground. Key on and 0.3 ohms to ground on positive cable. Is that because of the coils on the relays? Or is that not right? I didn't have time to check if it was like that on the Camaro, but the battery bleeding totally down in 20 minutes with the key on can't be right.

Another thing that I noticed that could be irrelevant is that the lights on the radio for preset 1 and 4 used to be dark, but now that I swapped out those 2 speakers the lights are now lit, which makes me think maybe the old speakers were shorted. I still have 2 more speakers to fix, but I am wondering if the blown speakers were causing a short to ground, but the check engine, ABS and brake lights came on after I fixed these 2 speakers.

[95 S_Trucker]

From my experience, 95% of the time I see a P0420 or P0430, It is the converter, not the oxygen sensor.

At 240,000, I'd say it needs one.

I have seen P0420/P0430 show up after a converter replacement. That happens when someone puts in a puny little converter that was 1/3 the size of the oem converter.

[68C15]

To test for parasitic draw you need to measure amps between negative cable and battery. Wait about 45-60 minutes for all modules to go to sleep (shut down). Do that and report back. I regularly see vehicles in that age group with draws in the .015-.050A range. You will NOT see this in a needle meter or test light, you must use a digital meter with the ability to test miliamps. When you key is on, each and every module is on. Modern batteries do not like that. If you plan to do this often, you may want to get a deep cycle battery

[68C15]

Originally Posted by 95 S_Trucker

From my experience, 95% of the time I see a P0420 or P0430, It is the converter, not the oxygen sensor.

At 240,000, I'd say it needs one.

I have seen P0420/P0430 show up after a converter replacement. That happens when someone puts in a puny little converter that was 1/3 the size of the oem converter.

Exactly!!!

OE converters are about $600 while aftermarket ones are about $200. You get exactly what you pay for, precious metals

[bufmatmuslepants]

The battery doesnt drain when the car sits, it sat for 3 days and was fine, it was just when I had the key on to hear the new speakers for a minute when I was putting the door panel back on, within 5 minutes the battery was DEAD. I want to pull the radio fuse and then see how long the battery can stay good, then I could narrow it down to something in the radio/speakers.

[bufmatmuslepants]

Update:

I was concerned about the oil pressure being lower cold than warm, and the low oil light and blamed sludge. If it was parked nose slightly up over night it wouldn't build any oil pressure for 10 seconds, and would tick loudly. If parked nose down it would build quickly but jump right to only 20, but warm had 40. I decided to change the oil again after 1000 miles and went out and beat the snot out of it on a lot of 0-90mph runs to get it hot. On the ride home it only had 10psi. I changed the oil with castrol gtx 10w30 (stupid move) and fired it up quick and went to bed. Went to work the next day and it only had 10psi, and after 5 miles it wasn't coming up, so I got scared and turned around. 1 mile later it dropped to 0 and was ticking loudly, but it was 4:30am and 26 degrees out and I accepted the fact that I would be swapping motors and said screw it, please make it home. 5 miles of 0 oil pressure and ticking loudly, as I pulled into my neighborhood it started coming back to 20 but I parked and took the no heat camaro to work bundled up in winter clothes.

Got home, started it, 0 pressure, got it on ramps and drained the oil. It was nasty. I used a coat hanger through the drain plug hole and got 8oz of brownie batter out of the pan but no metal shavings with a fridge magnet dragged through the oil. I would poke and prod a at the oil pickup and bottom of the pan a bit, then pour a little clean oil in the top to flush it out. Then I filled it with 5 quarts of 5w30 super tech and 1 quart of marvel mystery oil.

Started it up, straight to 40psi, but still ticking loudly. Had it running just long enough to back off the ramps, get out and try to listen which side, them kill it through the window. I cracked a beer, stared at the truck, finished the beer, then started it, and NO TICK!

Drove it 40 miles that night and it was fine. Then drove it 70 miles round trip to work the next day and changed the oil when I got home, and it was gross. Put in fresh castrol gtx 5w30 and another purolator filter, started it, it sounded good, great oil pressure at 45psi, and made the executive decision to put the wife, baby and dog in and head out at night 200 miles to VA beach for thanksgiving. It made it, great pressure and quiet, and made it home fine.

So the moral of the story is CHANGE YOUR OIL. I only used the MM oil for 100 miles because that stuff is strong and can eat away at seals and sludge that was plugging leaks, but it did the job. Ill change it again after 1000 miles and call it good. I'm very happy that I didn't have to do a motor swap, and really have a lot of respect for the 5.3. I think a lifter was not having enough pressure to pump it up, causing the noise, but the idiot gage probably was not accurate as there had to be some oil moving because it didn't seize.

Unfortunately while I saved $600 not having to swap motors, I didn't get out unscathed as my iPhone 6 went through the laundry in my dirty pants, so I'm out $600 anyways. Pictures of oil to come later from my laptop I saved them on before the phone got destroyed.

I did take the camaro battery with me to the airport to swap batteries when I get home from Cali if the draining issue is still there.

[68c10airstream]

Checking for a ohms reading with a circuit actively working won't be an accurate means of checking for poor connections. You need to do a voltage drop test on a live circuit.

The voltage drop test is basically taking a good multimeter and using it's leads in parallel in the dc voltage scale. Say you want to check the battery negative cable between the battery and frame. Scratch a shiny spot on the frame and a shiny spot on the battery negative terminal. Touch one lead on one shiny spot and the other lead on the other shiny spot. Now have someone crank it over (high amperage load) and take the reading. Ignore if the voltmeter shows a negative value, just remember the reading.

Rule of thumb is max allowable voltage drop per connection is .2 volts. The example test above should have a max reading of .4 volts (one terminal at the battery, and the other at the end of the cable at the frame.

In your prior posts you mention low idle. I suggest two things. If your engine is throttle by cable (no traction control) remove the idle air control (IAC) motor from the side of the throttle body (has a 4 wire plugin) and clean the pintle head and the bore that it sits in. The profile of the pintle head is specific for your application and needs to be clean.

The other item i suspect is a weak battery. If your meter is good quality and has glitch capture capabilities put it on the battery terminals and record min, max, and average during a start up of the engine. Look at the min value and if it drops below about 10.0 volts this needs to be corrected for a stable idle.

Here is the reasoning: The engine controller (pcm) basically does a reboot when battery voltage gets too low and the pcm looses the IAC counter reference number and has to start over. The idle relearn happens above 45 miles per hour as the pcm fully extends the pintle of the IAC to seat it in the bore (don't need idle circuit working at 45 mph) and when done it pulses the IAC the correct amount based on your application. Remember that the pcm can't see or read the IAC position because it's not equipped with a feedback positioner, so that is why it has to constantly recalibrate the IAC with every start up above 45 mph.

Also look at the ground located behind the driver's front tire at the body mount. The metal frame has a cup welded onto the outside of the frame and the body mount bolt goes up through it. Look on the backside of this cup and you will probably find 2-3 ground wires attached here, one i know is for abs. Fixed a few weird electrical issues cleaning up the eyelets and sanding the cup area shiny, once bolted back together then put grease over it and the threaded bolt sticking through the cup and forget that ever happening again because the grease prevent it from re-rusting again (prevents oxygen and salt from reaching it).

Been out of the field for many years but work on friends vehicles. Was an ASE mechanic for 30 years that spent my fair share of time fixing troublesome vehicles involving electrical and drivability issues

[bufmatmuslepants]

I have a Fluke and have been using that. I have 0.3 ohms to ground from negative post to frame, block and body when the motor is off. I have 25 ohms with the engine on. I used to have 60 until I cleaned all the negative grounds.

I did not notice a difference in idle quality or anything on the truck when I had the brand new camaro battery in there.

I had put the camaro battery back in the camaro to move it out of the garage to change the trucks oil, and luckily left it in there so when my oil pressure was at 0 I didn't have to swap batteries to take the camaro to work. I still had the old battery in the truck when we drove to VA beach and I THINK I had left the door open over night (or I opened it when I was loading the truck that morning and didn't notice it was already dead) but either way on Saturday the battery was dead enough to not crank the truck and I had to jump it to go home. When it did that it did reset the PCM because voltage was low enough and it cleared the check engine light, but did not reset the IAC because it didn't stumble like normal when I swapped batteries. Either way, whether it was low enough voltage to reset the SES or it cleared on its own, the check engine light has not come back on in over 200 miles. Usually it came back within 30 miles. The light was for LOW KNOCK SENSOR INPUT BANK 2 and CATALYST BELOW EFFICIENCY BANK 2. My guess is the low oil pressure before was not pumping the lifters enough, causing a little tick enough for the knock sensor to pick up, causing it to pull timing on bank 2, causing incomplete fuel burn, causing the O2 sensor to pick up more oxygen, causing the cat code.

I did clean the ground on the EBCM on the body mount cup, but did not replace the bolt with a through bolt and a nut, so it might not be making good connection. Since I cleaned that ground, the ABS and BRAKE lights come on MORE than they used to, so I do need to replace it with a nut and bolt and clean it again and see if that helps.

I DID get another CHECK ENGINE OIL LEVEL light, even after the sludge removal. It would not clear with a quick shut off of the engine and restart like it had in the past, but did clear after sitting overnight, and the oil level looked ok but it was dark out. That one is still strange. I have not read the codes to see if I have a code for the knock sensor or cat pending, but I will when I get back from Cali this weekend.

I got a new head unit from my brother that I will swap in and I will disconnect the 1 bad speaker left and see if that was a short. The fact that when I changed 2 blown speakers and my 1 and 4 preset lights started working again was strange.

The dash light dimmer switch is another suspected short, as it does not dim, it has to be all the way up, just barely balanced before the dome lights come on to have the dash lights work at all. I need to change that too, or disconnect it and see if that changes anything.

[68C15]

I repeat;
When you key is on, each and every module is on. Modern batteries do not like that. If you plan to do this often, you may want to get a deep cycle battery