Service 4wd and check engine light

[RyanbabZ71]

2000 Chevy Blazer 4wd with autotrac (moms vehicle). About 2 yrs ago she had some motor for the 4wd system replaced.

 

Lately the service 4wd light has been coming on (flash on and off briefly).

 

Yesterday the lights started flashing along with the check engine light.

 

She said it looked like a christmas tree.

 

Any ideas?

[Bish]

2000 Chevy Blazer 4wd with autotrac (moms vehicle).  About 2 yrs ago she had some motor for the 4wd system replaced.

 

Lately the service 4wd light has been coming on (flash on and off briefly). 

 

Yesterday the lights started flashing along with the check engine light. 

 

She said it looked like a christmas tree.

 

Any ideas?

 

<{POST_SNAPBACK}>

 

 

 

When my switch failed, many lights were lit.

 

Be careful with a flashing check engine light! On most vehicles, a flashing check engine light means you are actively misfiring and damage WILL occur if driven for any length of time.

 

Best bet would be to pull the code(s). That should point you in the right direction.

[71GMC_3/4T]

I have a feeling the two are not related, but I may be wrong.

 

The Service 4WD message is usually because the switch module went bad. Mine had cracked solder joints inside.

 

The Check Engine light is probably being caused by something else. Like Bish says, have someone pull the code and find out what it is before you cause damage to the engine. A lot of autoparts stores in this area will pull the codes for free. You'll probably only get numbers/letters, but you can post on here and someone will tell you what it means.

[RyanbabZ71]

Be careful with a flashing check engine light! On most vehicles, a flashing check engine light means you are actively misfiring and damage WILL occur if driven for any length of time.

 

I received some more info today. I told my mom when I was in town last week to try and engage all of the buttons while in park in the driveway (2wd, 4 hi, 4 lo, auto 4wd). All of them engaged except when she pressed 4 lo (not moving and the truck in park) the light flashed a few times (5???) then went back to 2wd (didnt engage) then some of the lights on the dash stated to flash (check engine light etc). THose havent come back on either has the 4wd service light.

 

HMMM bad switch?

[BRZ71]

Be careful with a flashing check engine light! On most vehicles, a flashing check engine light means you are actively misfiring and damage WILL occur if driven for any length of time.

 

I received some more info today. I told my mom when I was in town last week to try and engage all of the buttons while in park in the driveway (2wd, 4 hi, 4 lo, auto 4wd). All of them engaged except when she pressed 4 lo (not moving and the truck in park) the light flashed a few times (5???) then went back to 2wd (didnt engage) then some of the lights on the dash stated to flash (check engine light etc). THose havent come back on either has the 4wd service light.

 

HMMM bad switch?

 

<{POST_SNAPBACK}>

 

 

 

 

Trans has to be in N for 4 low to engage

[RyanbabZ71]

not for autotrac anything like 5mph and less it will engage.

[71GMC_3/4T]

But it probably won't do it in Park as the driveline could be in a bind. It also has to go through transfer case neutral to get to 4 low.

[OUMike]

Be careful with a flashing check engine light!  On most vehicles, a flashing check engine light means you are actively misfiring and damage WILL occur if driven for any length of time.

 

Actually thats not entirely true. Maybe just on OBS pickups, but I just recently had a misfire problem and NO check engine light. A technichian told me check engine light is mainly due to things sensor or emssions related. O2 sensors, running too hot, fuel pressure, alternator volts are things I've noticed effect check engine light.

[ness5575]

not for autotrac anything like 5mph and less it will engage.

 

<{POST_SNAPBACK}>

 

 

 

True, but not quite.

you have to be in 4hi, the transmission must be in neutral, and you must be moving less than 5 mph.

 

if not, it will do just as she said...

[Bish]

Be careful with a flashing check engine light!  On most vehicles, a flashing check engine light means you are actively misfiring and damage WILL occur if driven for any length of time.

 

Actually thats not entirely true. Maybe just on OBS pickups, but I just recently had a misfire problem and NO check engine light. A technichian told me check engine light is mainly due to things sensor or emssions related. O2 sensors, running too hot, fuel pressure, alternator volts are things I've noticed effect check engine light.

 

<{POST_SNAPBACK}>

 

 

 

 

Agreed that the Check Engine light generally means emmissions. Now regarding a FLASHING Check Engine light, on 2 vehicles I have owned (1 Ford, 1 Chevy), the manual specifically stated if the Check Engine light is flashing, you have a constant misfire condition and you should pull over and NOT drive the vehicle. I have not read that in my Tahoe manual but then again, the operators manual on most cars is a joke these days. More to protect against liability (when using cruise control, remember, you still need to steer the vehicle) and as such have become a waste of paper.

 

Both vehicles did this after a car wash and both went back to normal when they dried out. I would not likely take a chance and drive with a flashing engine light. Worse case scenario it is misfiring and you could burn a hole in the piston.

[BRZ71]

not for autotrac anything like 5mph and less it will engage.

 

<{POST_SNAPBACK}>

 

 

 

True, but not quite.

you have to be in 4hi, the transmission must be in neutral, and you must be moving less than 5 mph.

 

if not, it will do just as she said...

 

<{POST_SNAPBACK}>

 

 

 

 

 

AutoTrac is 4 HI when it engages. If you truck goes into 4Lo in P something is very wrong! Try to put a manual Tcase into 4 lo in P, it makes lots of interesting noises, at leat the one I tried a year ago. You do not have to be in 4 hi to get to 4 Low. You must be in N stopped or moving less than 5 MPH. I go from 2 HI to 4 LO all the time. The gears seem to mesh together a little smoother and the Tcase makes less noise if you are moving.

 

If you had to be in 4hi, moving, and in neutral there are several mud holes I would still be stuck in!

[BRZ71]

From the Manual

 

Shifting into 4HI or Auto 4wd

 

Press and release the 4 HI or Auto 4wd Switch. This can be done at any speed (except when shipfing from 4LO), and the indicator light will flash while shifting. It will remain illuminated when the shift is complete.

 

Shifting into 2 HI

 

Press and release the 2HI switch. this can be done at any speed

(except when shifting from 4 LO)

 

Shifting into 4 LO

 

To shift to 4LO, the ignition must be in RUN and the vehilce must be stopped or moving less than 3 MPH with the transmission in N. The preferred method for shifting into 4 LO is to have your vehicle moving 1 to 2 MPH. Press and release the 4 LO switch. You must wait for the 4LO indicator light to stop flashing and remain illuminated before shifting your transmission in gear.

 

If the 4 LO switch is pressed when your vehicle is in gear and/or moving, the 4 LO indicator light will flash for 30 seconds and not complete the shift unless your vehilce is moving less than 3 mph and the transmission is in N. After 30 seconds the transfer case will return to the setting last chosen.

 

Shifting out of 4LO

 

To shift from 4 lo to 4HI, Auto4wd, or 2 HI your vehicle must be stopped or moving less than 3 MPH with the transmission in N and the ignition in RUN..............You must wait for the 4 HI, Auto4wd or 2hi indicator light to stop flashing and remain illuminated before shifting your transmission into gear.

 

Shifting Into Neutral (condensed a little from the manual)

 

Put on the parking Brake (VERY VERY IMPORTANT)

 

Put Transmission in N

 

Sumultanesouly Press and hold 2HI and 4LO for 10 seconds

 

The red N light will come on when the shift is complete

 

Shift Transmission to R or one second, then to D for one second.

 

Turn off Ignition

 

Place transmission in P

 

Release the parking Brake

 

Hook the truck up to your motorhome, and go on a trip.

 

Shifting out of neutral

 

Put parking brake on

Shift Transmission to N

Put key in ignition, and turn to run but don't start the truck

Press desired mode

Once shift completes red light will go out

release the parking brake

Now you can start the truck and drive away

[RyanbabZ71]

New info.

 

Found out today (I find out bits and pieces sorry).

 

When driving the truck will engage 4wd on its own. I havent heard of this one. Back a few yrs ago the TCCM was replaced because of a service 4wd light. Well my dad talke to gm (local dealer) and they said it sounds like the same problem. HMMM