Hello everyone,
The day b4 Xmas eve I purchased my 99 Blazer. Im happy with my purchase but ran into a 2 problems. I'm a full time mom of 4 so I really need my vehicle. (I've searched the forum but can't find anything specific to my problem) So here it is, today the service engine soon light came on. So I went to Autozone to see what that ment. The hand held diagnostic tool said

P1875 Low Switch Circuit Fault (4L60-E,4L65-E,4L80-E)) it says this code twice

P1870 Transmission Component Slipping (4L60-E,4L65-E,4L80-E)

Please anybody feel free to welcome me to Blazerforum.com with some suggestions. Does the P1870 transmission mean I have a bad transmission? The guy/kid at autozone said bcuz the 4L60 was on all the codes that when I fix the switch/4wd button that the other code will disappear. But he was no more than 20 so I'm hoping he's right but again any help will be greatly appreciated!

Lisa

 

Lisa,

I happen to have a 1999 Blazer too and also the repair manuals.

The first thing to do is check the transmission fluid level. That can cause any number of problems.

Failing that from my quick reading there could be a bad connection in the control circuitry that is causing the fault. (P1875 error)

Does the transmission and transfer case seem to work fine in 2-Hi or 4-Hi? I ask because the fault can be associated with the 4-Lo operation which few of use very often. (P1875)

Have you tried purposely going in and out of 4Hi and 2Hi?

I've attached pictures from my manual that might help you or someone else you know or finds this post who knows how to interpret this material.

Good Luck!

Christine

P.S. TCC = Torque Convert Clutch and VCM = Vehicle Control Module

 

the control for 2 hi and 4hi doesn't work. I'm thinking the transmission is slipping bcuz of the Control case/buttons not working. the transmission only slips in 1st and 2nd gear once in third it's perfect. Thank you for your help this forI'm is all I have since my dad passed. He could literally listen to a sound of the car and tell u what was basically wrong or what could be wrong. I truly do miss that man! but any who thank you

 

Lisa,

Yes, there could be a problem with the transmission. I'm not familiar with this particular one but I wouldn't be surprised if 1st and 2nd are somehow combined.

No matter what, be sure to try the simplest thing first; the transmission fluid level. I've heard of people can smell the fluid on the dip stick and tell if it has been over heated. Do this before you add any more. If it has been overheated, especially if it is low that could mean that you should look out for a malfunctioning transmission. No matter what, at least put in more fluid as necessary to bring it to the right level. The fluid is integral to how it shifts from one gear to another.

The transfer case can also be low on fluid. Depending on the type of transfer case, it can take special fluid. If you have an Auto 4WD setting on the transfer case selector in addition to 4Hi, 2Hi and 4Lo, then it likely takes the special fluid.

I mention the special fluid so that if you take it to a place like Jiffy lube you can tell them to use the special stuff.

Be sure to post what you find out.

If adding the transmission fluid seems to make things run better, you should plan to get the transmission fluid system flushed and the transmission filter replaced. It can cost several hundred dollars but it is likely that it has never been done and you will likely never need to do it again.

Check your owners manual for more details. You should be able to download one if you don't have one. (That is what I had to do.)\

Good Luck (and Happy New Year!)

Christine

 

The transmission fluid is pretty clean the previous owner did a flush/change idk if he changed the filter tho. We changed the belt cuz it started to make a squeal. it still seems to shift slow in 1st and 2nd but (sounds strange I know) not as much like it seemed to help. The fluid level seems good. But I'm going to go to blacks tire tomorrow to hsbe the fluid checked to be sure. They normal check my fluids for me when I ask them there nice people up there. I'm glad u told me about the special fluid I'm going to have that checked as well. I'll let you know what happens thanks so much!

Lisa

 

Lisa,
Couple of things;
1. I assume that the 4wd switch does not light-up and this is not an uncommon problem. Usually all that is required is to reflow the solder joints on the circuit board within the switch assembly. Do not know if this is something you can do or if you know someone that could, or just get a new switch assembly.
2. Another thing to check is the connector on the TCCM (Transfer Case Control Module). It is located under the small kick panel in the passenger foot well. The cover just pulls off and I think there is one bolt holding the TCCM. Just need to remove the electrical connectors and see if there is any corrosion on the connectors or the TCCM circuit board. Get some electrical contact cleaner and clean both.
3. The previous owner changing the trans fluid was likely to hide the slipping problem due to either low and/or burnt fluid. One problem our Blazers have is if the rear trans seal leaks the trans fluid goes into the transfer case. Vacuum lines connected to the transfer case will suck up the trans fluid when the transfer case is over full...and then trans fluid gets into the HVAC system and causes all sorts of problems. Checking the transfer case fluid level as Christine suggest is needed. There is no dipstick though and only way to do this is to have Blazer level and remove the fill plug. The fluid should just be at the fill port, if fluid pours out then likely the rear trans seal is gone and trans will need to come out.
Does the HVAC controls work? Do you get heat and are able to direct air flow?
4. The trans slipping code is not something I have ever dealt with. The slipping could be that the fluid is just low or the trans need work as the manual lists.

Good luck and keep us informed as to what you find out.

 

Note - Excessive Acronyms in this post, but what else can you do?

P1870 is likely due to a worn TCC regulator bore - a common problem in the 4L60E transmission. The P1875 is probably not related to the P1870. For P1875 looks like your PCM is detecting the transfer case is not going into either the low or the high range where it thinks it should be. It need to know this to adjust the harshness of the shifts. Should be some sort of electrical issue outside of the transmission.

Fluid is probably new from taking off the trans pan to attempt fixing the P1870. Probably the reason previous owner sold the vehicle. The thing detected as slipping is the torque converter clutch (TCC) in the torque converter, not the forward/reverse clutches in the transmission.

You can read about the P1870 in this article. Note that your Blazer TCC has both PWM (Pulse Width Modulated) and EC3 (Electronically Controlled Converter Clutch) to apply it smoothly and also maximize fuel mileage. The vehicle (PCM) computer expects a specific amount of slippage of the TCC, but within a certain range of slippage (hence the code). Mentions the right way and the wrong way to fix the most common reason for the code and SES light. Note that just using the spring trick raises converter pressures enough to potentially take out the engine thrust bearing and I would not recommend it.

20 Years Later: What?s New with 4L60-E PWM Modifications - Sonnax

Will either code/problem leave you stranded driving around town? Probably not. Would I take a long trip without the TCC engaging correctly (especially in overdrive)? No.

If the vehicle has been driven for extended periods with TCC slipping excessively, it may require converter replacement for proper operation. No way for anyone to know until repairs are effected. Although hydraulic repairs should be able to be done in the vehicle, converter replacement (if needed) requires the transmission to be removed from the vehicle. On a 4WD Blazer this is not trivial (not nearly as bad on a 2WD).

So if you want to fix it, pick a good trans shop and let them have a go at diagnosing and potentially doing hydraulic repairs. If it then requires a converter to eliminate the codes and SES light, you will have to decide if the vehicle and it's intended use is worth it.