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Discussion Starter #1 (Edited)
I'm pretty sure that's what my local mechanic said when I looked up the flashing code for good old ODB1 diagnostic. He didn't want to go any further than translating the code as he didn't want to chase down electrical gremlins. So I was kind of stuck and took a chance on a local shop 2 blocks over from my office. Talked to the shop owner, and he referred me right next door as he said they have an excellent wiring guy. Walked over and described my problem ( CEL, fans come on right away on engine start, even when ice cold ), and replacing the passenger side fan after the previous owner hit something that dented in the lower radiator/fan support causing the fan to seize.

I did my best to reconnect the harness properly during the R&R of the seized fan, but still have this issue.

I will replace the fan blower resistor as after the critter junk was cleaned out from my HVAC I have only 3 of 4 fan speeds, Low, S2, S2 (same speed as 2nd setting) High.

Really looking forward to having this fixed so I can figure out why the trunk fills with water when it rains... =/
 

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Walked over and described my problem ( CEL, fans come on right away on engine start, even when ice cold ),/
check your ECT (temp sensor) on front of water pump and the wiring going to it

courtesy of shbox.com

"The PCM gets it's temp readings from a sensor that is in the water pump. It uses two wires. If the reading the PCM receives is inaccurate, the fans may not come on at the correct time. The PCM also uses this temperature for lookup in calculation tables. If there is a problem that causes the reading to be always low (cold), the PCM will add extra fuel. This can cause hard starting when warm and an overly rich condition when running.

The gauge gets it's information from a sensor that is in the driver's side head. It uses one wire. Inaccurate gauge readings can be from this sensor or it's wiring (the wire burned on a header pipe is common). The temp that the PCM sees can be monitored with a scan tool and compared to the gauge reading. They should be close, but don't expect them to be "perfectly" synchronized.

The temperature sensors in the water pump and the cylinder head are not the same. I recommend genuine GM/ACDelco for replacements.

The fans are programmed to come on when the a/c is turned on. A/c Pressure monitoring sensors feed the PCM info and depending on the situation, the PCM may command the fans off for brief periods. If your a/c is broken or operation inhibited because of low refrigerant, the fans will not come on when the a/c is turned on (but will still operate by engine temp). Also, when the car reaches sustained higher speeds, the fans may be commanded off so incoming air can flow through the radiator unimpeded and provide the cooling needed.

Fans will come on when field service mode is initiated and also when the SES lamp comes on. The PCM does this when certain (most) DTCs are detected to protect the engine from a situation where it may overheat."

use a DVM to measure the resistance of the temp sensor on the water pump per this chart

4th Gen LT1 F-body Tech Articles
 

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Discussion Starter #3 (Edited)
Thanks! Always want to take a stab at the DIY method for cost savings and learning.

On second thought, I just read through the information provided and decided that beyond checking for a disconnected/burnt wire on a visual inspection I'd rather pay a pro.
 

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If you have a obd reader that can display live data, you can see what it shows for the ECT temperature. If it's looking valid, you probably don't need the DVMM to buz anything out.


For your trunk water, check the seams at the top of the quarter panels where they meet the roof. It's about 6 inches long. The painted caulking there dries up, cracks and lets water in.
 

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Discussion Starter #5
Thanks, no reader, and this is ODB1, just flashing indicator. I will have a look at the trunk as well.
 

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OBD 1 will give you live data too in case you didn't know. And it would show IIRC like a huge negative temp if there is a break in the circuit or bad sensor.
 

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Thanks! Always want to take a stab at the DIY method for cost savings and learning.

On second thought, I just read through the information provided and decided that beyond checking for a disconnected/burnt wire on a visual inspection I'd rather pay a pro.
It takes 5 seconds to check sensor with a DVM for ohms....but if you want to pay someone to do that fine.….but that person would need to know wtf the ohms should be....assuming he even knows the WP ECI sensor can cause both fans to come on at cold start

This may not be your problem but for less effort than it takes to unscrew a gas cap to check....
 

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Discussion Starter #8 (Edited)
Yep, I get it, but I'm at the point where I just need it fixed - no matter how simple it is to check X, Y, Z. I was assured their 'wiring guy' is the best and knows his bleep. So we'll see how it goes.

I couldn't see any evidence of bad caulk on the rear quarters, just a little crack in it in the top of the 2nd pic. Will look at this area more closely and check for moisture underneath that area.

Also changed the oil and put new rubber on my 'other' baby.





 

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I'm pretty sure that's what my local mechanic said when I looked up the flashing code for good old ODB1 diagnostic. He didn't want to go any further than translating the code as he didn't want to chase down electrical gremlins. So I was kind of stuck and took a chance on a local shop 2 blocks over from my office. Talked to the shop owner, and he referred me right next door as he said they have an excellent wiring guy. Walked over and described my problem ( CEL, fans come on right away on engine start, even when ice cold ), and replacing the passenger side fan after the previous owner hit something that dented in the lower radiator/fan support causing the fan to seize.

I did my best to reconnect the harness properly during the R&R of the seized fan, but still have this issue.

I will replace the fan blower resistor as after the critter junk was cleaned out from my HVAC I have only 3 of 4 fan speeds, Low, S2, S2 (same speed as 2nd setting) High.

Really looking forward to having this fixed so I can figure out why the trunk fills with water when it rains... =/
You are aware that the HVAC fan has nothing to do with the engine fans, don't you?

Just wondering why blower resistor, 3 of 4 speeds, etc., was inserted in your OP.
 

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Discussion Starter #10
Yes, I'm aware of that. Was just commenting on the status of my HVAC regarding an old post from last year.
 

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Yep, I get it, but I'm at the point where I just need it fixed - no matter how simple it is to check X, Y, Z. I was assured their 'wiring guy' is the best and knows his bleep. So we'll see how it goes.
…..well you asked the ? on a forum...and I replied with what is a fairly common cause of your "both fans on at cold start up". The check is simple, if you have a DVM. Or you could just buy another ECT sensor and put it in

the "wiring guy" may be the best guy on the planet to do wire repair but will need to know before doing anything to check resistance of the sensor and if he checks it would need to know the correct ohm per temp so if he doesn't I would encourage you to provide the information (link I posted)

again you will spend more time, let alone $, taking it to this guy to check the sensor first...but I digress.

the ohm test would rule in/out the sensor.

connectors that are removed for servicing the car. like replacing a WP for example, can get the wires in/to them messed up if one pulls on the wire while trying to remove a connector or the wire at the connector just finally succumbed to heat/use. Typically a close visual inspection or using the continuity function of a DVM to probe terminal and a few inches above the connector to reveal if continuity is good in the wiring/terminal at the connector will show if wiring is good

Given the location of the ECT sensor….this is a extremely easy one to check
 

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I couldn't see any evidence of bad caulk on the rear quarters, just a little crack in it in the top of the 2nd pic. Will look at this area more closely and check for moisture underneath that area.
The seam is up at the roof. Not where you're showing in the pictures. ANY cracks up there will have water running along the underside and drip where you show in the pictures. But it's coming from the top.
 

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Discussion Starter #14 (Edited)
Ok, I will document this in the proper sub forum as this side topic doesn't belong here. Do you recall any images posted that show the cracked caulk?

[Edit found existing thread in Exterior sub forum]
 

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Discussion Starter #15
Had to update this thread as I got my 95 SS back from the shop, and they couldn't figure out how to get the fans to stop running in failsafe mode all the time. The mechanic did his best to test all the wiring and connectors for proper voltage and visual inspection for loose/corroded/stripped wires as well. They had a look at the forum post for troubleshooting fans (the one that includes the ECT Temp vs Resistance Values chart). Given the Opti is original and car now has 130k on it, it's a good time to replace it. The CEL is throwing codes for a faulty Opti, so I'm having the ebay rebuild service done and replacing the water pump, and required seals myselfl. I was expecting a huge bill for all the work that was done while they had the car, which included replacing the ECU (which I provided), troubleshooting the fan issue, state inspection, and replacing faulty windshield washer fluid motor was just 242$. Car runs much better now, as before it would sometimes stumble as if it wasn't getting fuel. If we still have CEL after replacing the Opti and the fans are on, I can bring it back and they will check the code and see if they can chase it down. Luckily in NH you can still pass inspection with a CEL for a vehicle that is so old.

At this point I'm wondering should I just spend 12$ and replace the temp sensor in the water pump? This amazon link uses the exact same picture as the one listed on Rock Auto;

https://www.amazon.com/Delphi-TS10075-Engine-Coolant-Temperature/dp/B000CGM9O2/

https://www.rockauto.com/en/moreinfo.php?pk=1111888&cc=1049699&jsn=11746

I know that the die hards on this forum always recommend performing a proper diagnosis and systematic troubleshooting method to test parts, but when it's a cheap and simple replacement I'm not averse to replace something while I've got the tools out and and am working on it.
 

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At this point I'm wondering should I just spend 12$ and replace the temp sensor in the water pump? .
did you ohm the sensor and use the chart that notes what temp=ohm it should be?


I doubt the opti has anything to do with the fans staying on

If sensor checks out using your meter I would back probe the wires going to the sensor all the way to PCM.

You confirm the fan relays are not frozen "on"?? (and also read the contacts they plug into are not melted and shorted...which was a TSB)


Spending $12 on a new sensor is fine if you want. You should be able to "quickly" install it after unscrewing the old one without much coolant loss so you would not need to bleed cooling system
 

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Discussion Starter #17 (Edited)
Agreed, the Opti shouldn't have anything to do with the fan issue, but just clearing codes systematically. I have mentioned before that the previous owner appears to have gone off roading and the passenger side fan was stuck as the lower support was jammed up into the fan preventing it from turning and it burned out. I replaced it, but since then they have always been always on. I'll see if I can get my hands on a DVM to do some testing.
 

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At this point I'm wondering should I just spend $12 and replace the temp sensor in the water pump?
Yes. Also do a 'jiggle & wiggle test'. I once had a problem where my engine would stumble every time I hit a bump or made a right turn without stepping on the gas. Turns out the wire would behave, unless I grabbed it and moved it an inch away from its resting position.
 

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You confirm the fan relays are not frozen "on"?? (and also read the contacts they plug into are not melted and shorted...which was a TSB)
BALLSS


"frozen on" relays would make the fans run all the time key on or off. The fan relay feed is hot at all times.. Melted contacts in the box are more likely to prevent the fans from starting. Give the shop some credit, most will start by trying a new relay. It would do the OP no harm to try a borrowed or new relay but it probably will not help. If you can hear or feel the relays click and the fan comes on you do not have to look at the relay and fan part of the circuit.



which included replacing the ECU
ace72ace Without OBDI live data you are wasting resources. If the PCM is showing the engine's temperature correctly then check if the PCM is turning on the fans. The OP will have to focus on PCM output to the fans and the possibility that the original owner has bypassed the PCM or the remote possibility the PCM is damaged. IE: PCM shows fans off but the outputs are grounded and turn on the relays.It is unlikely that two PCMs are bad.



The reason throwing parts at it without live OBDI data is bad is the problem could be related to a bad pressure sensor on the freon line, A/C commanded on or some other cause that makes the PCM turn on the fans. Engine coolant temperatures are NOT the only thing that can force the fans on.


ace72ace if you want to get the most out of your repair dollar find a shop with OBDI live data and a reputation for being able to do diagnostics. Get a FSM it may help.
 

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Discussion Starter #20
Thanks, that's the hardest part finding a shop with ODB1. I have the FSM if it needs to be referenced.

Interesting to note, my AC isn't holding a charge. It wasn't blowing cold when I first got it, and I suspect the seals have dried out. I recharged it last year but now it's not cold at all, just another thing to fix... sigh.
 
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