Tranny wont downshift
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Tranny wont downshift - 10/8/2007 6:31:09 AM
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bitbandit
Posts: 102
Joined: 9/16/2007
From: Brigham City, UT
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my transmission will not down shift, when i start going it shifts through all the gears and gets to OD by the time i am going 35-40 MPH. and when i lay the pedal down it very slowly starts to gain speed, but will not down shift. also when going up a hill it will not down shift unless i do so manually. when i come to a stop it will go back down to 1st. has anyone had this problem or know what is causing this?
2001 ZR2 Automagic
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RE: Tranny wont downshift - 10/8/2007 9:51:30 AM
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rriddle3
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From: Fort Worth,Texas
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Not being a tranny man, the only thing I can imagine that might be user serviceable is that the manual linkage is out of adjustment. Beyond that it is probably internal and a job for an auto trans shop. BTW, have you checked your fluid level and are you getting any DTC's?
< Message edited by rriddle3 -- 10/8/2007 9:55:49 AM >
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RE: Tranny wont downshift - 10/8/2007 10:02:57 AM
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swartlkk
Posts: 14308
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From: Waterloo, NY
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On a 2001, this is all electronically controlled. I suspect there is a problem with one or more of the sensors on the engine. The PCM uses the requested torque value calculation to determine the appropriate gear to be in during operation. When you push on the throttle, this is communicated to the PCM through MAP, MAF, and TPS sensor data which all communicate that more torque is being requested. These sensors should produce trouble codes if operating outside of acceptable limits. If no DTCs are present, then this may be a problem with the PCM, but the diagnostic steps are pretty involved and require a Tech 2 scantool or equivalent.
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Kyle-
2004 Rainier
1970 Chevelle - Resto
1974 K5 Blazer - Resto
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RE: Tranny wont downshift - 10/8/2007 10:05:06 AM
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bitbandit
Posts: 102
Joined: 9/16/2007
From: Brigham City, UT
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Yeah my fluid is a champ, just changed the filter and added new stuff, and did the whole routine the manual says to do.
DTC's = Check engine codes ?
would a clogged CAT cause this?
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RE: Tranny wont downshift - 10/8/2007 10:15:37 AM
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swartlkk
Posts: 14308
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From: Waterloo, NY
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DTC == diagnostic trouble codes so yes, check engine codes.
How does the truck accelerate up through the gears? How is your mileage? A clogged cat would limit higher RPM power by (in most cases) severely limiting exhaust flow.
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Kyle-
2004 Rainier
1970 Chevelle - Resto
1974 K5 Blazer - Resto
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RE: Tranny wont downshift - 10/8/2007 10:19:28 AM
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bitbandit
Posts: 102
Joined: 9/16/2007
From: Brigham City, UT
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the SES light was on yesterday and i was goign ot take it in and get the codes but it was off when i go in to go to work, it shifts smooth but its a little doggy, when i hammer down on teh pedal from a stop it starts going good then it just goes up through the gears, so by 35-40 its in od, the RPMS hardly get above 2500-3000 when i am flooring it
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RE: Tranny wont downshift - 10/8/2007 10:23:40 AM
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bitbandit
Posts: 102
Joined: 9/16/2007
From: Brigham City, UT
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i just got my motor put back together on saturday night, and that was the first time i drove it, i bought it with a bad Intake gasket, so i never test drove it since i didnt want to mess the motor up any more than it may have been. if its not in gear it revs up good but when its in gear it does not.
also took about 1/4 tank of gas to go 110 miles, not sure how the milage is quiet yet.
< Message edited by bitbandit -- 10/8/2007 10:26:36 AM >
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RE: Tranny wont downshift - 10/8/2007 10:42:51 AM
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swartlkk
Posts: 14308
Joined: 5/1/2005
From: Waterloo, NY
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From your description, it is possible that this is being caused by a failing or plugged cat (but again, this should trigger an SES light). But the fact that it shifts the same regardless of throttle position would lead me to believe that the PCM is missing part or all of the picture. You could diagnose a failing or failed cat by removing one of the O2 sensors in front of the catalytic converter and disconnecting the other. This will cause the truck to run in open loop mode and will set O2 sensor DTCs, but it will run. If the truck runs better with the O2 sensor removed, then you have a plugged cat. BTW, it will be loud so don't run it long!
I just posted the checks for determining if you have a faulty TPS sensor in another post. You should have a ground, +5VDC, and a signal wire on the TPS sensor located on the driver's side of your throttle body. If you find that you do not have the +5VDC reference, then something is wrong with the PCM as this is a PCM fed reference voltage. The gray wire should be your +5VDC reference, black == ground, and the dark blue will be your signal back to the PCM. These colors are correct for a 2000 engine, but I think they should work for yours as well. If you find that the voltage is correct on the gray wire, then move to probing the dark blue wire.
Here is a link to a pdf file that explains position sensors: Position Sensors - courtesy of Autoshop101.com
However, when the PCM detects a malfunction with the TP sensor circuits, one of the following DTCs will set:
DTC P0121 Circuit Performance Malfunction
DTC P0122 Circuit Low
DTC P0123 Circuit High
DTC P1121 Intermittent Circuit High
DTC P1122 Intermittent Circuit LowSo it looks like if there are no DTCs set, this may not be your problem.
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Kyle-
2004 Rainier
1970 Chevelle - Resto
1974 K5 Blazer - Resto
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RE: Tranny wont downshift - 10/8/2007 11:11:21 AM
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Hanr3
Wheels & Tire Moderator
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I was going to suggest your governor is sticking. But it sounds more like engine problems.
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'93 S10-Blazer 4x4x4 - Sons DD, engine swap is done.
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RE: Tranny wont downshift - 10/8/2007 11:22:43 AM
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bitbandit
Posts: 102
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From: Brigham City, UT
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ok so, when i went to lunch the SES light was on so i stopped in at AutoZone and got the following codes
p0118, p0122
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RE: Tranny wont downshift - 10/8/2007 11:35:37 AM
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bitbandit
Posts: 102
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From: Brigham City, UT
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so looks like i need to get the codes taken care of and should clear up my shifting problem, i will ahve ot get that done and let you guys know. you guys are champs, thanks for all the help
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RE: Tranny wont downshift - 10/8/2007 11:42:26 AM
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swartlkk
Posts: 14308
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From: Waterloo, NY
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Hmm..
P0118 - Engine Coolant Temperature (ECT) Sensor Circuit High Voltage
P0122 - Throttle Position Sensor Circuit Low Voltage
So it seems that something is amiss with one or both of these sensors. Both of these sensors share a ground back to the PCM so it could be a wiring problem that is feeding voltage through the ground on the TPS/ECT that is causing a low readin on the TPS due to its configuration, and a high reading on the ECT. With the ignition off, check for continuity to ground on the black wire from both sensors. Then with the ignition on, check for continuity to the positive terminal of the battery. Inspect the harness from the ECT & TPS for any signs of damage. If you notice a damaged harness covering, open it up and inspect the wires inside.
quote:
The Engine Coolant Temperature (ECT) sensor is a thermistor, a resistor which changes value based on the temperature, mounted in the engine coolant passage. A low coolant temperature produces a high resistance of 100,000 ohms at -40°C (-40°F) while a high temperature causes a low resistance of 70 ohms at 130°C (266°F) .
The Vehicle Control Module (VCM) supplies a 5 volt signal to the engine coolant temperature sensor through a resistor in the VCM and then measures the voltage. The voltage will be high when the engine is cold. The voltage will be low when the engine is hot. By measuring the voltage, the VCM calculates the engine coolant temperature. The engine coolant temperature affects most systems the VCM controls. The scan tool displays the engine coolant temperature in degrees. After engine startup, the temperature should rise steadily to about 90°C (194°F) , then stabilize when the thermostat opens. If the engine has not been run for several hours or overnight, the engine coolant temperature and the intake air temperature displays should be close to each other. When the VCM detects a malfunction in the ECT sensor circuit, the following DTCs will set:
* DTC P0117 Circuit Low
* DTC P0118 Circuit High
* DTC P0125 Excessive Time to Closed Loop
* DTC P1114 Circuit Intermittent Low
* DTC P1115 Circuit Intermittent High
The above DTCs contain a table in order to check for sensor resistance values that are relative to temperature.
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Kyle-
2004 Rainier
1970 Chevelle - Resto
1974 K5 Blazer - Resto
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RE: Tranny wont downshift - 10/8/2007 9:19:36 PM
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Hanr3
Wheels & Tire Moderator
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Got any squirrels eating nuts on your engine?
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'87 S10-Blazer - SOLD
'93 S10-Blazer 4x4x4 - Sons DD, engine swap is done.
'00 S10-Blazer 4x4x4 - My
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RE: Tranny wont downshift - 10/9/2007 5:24:06 AM
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bitbandit
Posts: 102
Joined: 9/16/2007
From: Brigham City, UT
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cant say that i do
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RE: Tranny wont downshift - 10/9/2007 6:46:50 AM
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bitbandit
Posts: 102
Joined: 9/16/2007
From: Brigham City, UT
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if my Engine Coolant Temperature was having troubles wouldnt that effect my temp gauge in the dash? it seems to be working properly, starts out cold and as i start driving and it warms up it moves its way up to just below 210.
a TPS is $35 and a ECT is $15, but i am wondering if the gauge works if i should replace the ECT. i looked at my wires last night didnt see any damage, did not test the TPS to see if it is faulty yet, gets dark to soon this time of year : (
also should i have squirrels eating nuts on top of my engine? i thought they took the squirrels out of this motor and put in some racoons?
/my lame attempt to make a funny
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RE: Tranny wont downshift - 10/9/2007 7:04:24 AM
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swartlkk
Posts: 14308
Joined: 5/1/2005
From: Waterloo, NY
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Two different sensors. The sending unit for the gauge is in the side of the head on the driver's side. The ECT is on the intake.
Tim (hanr3) had a bout with some squirrels chewing on his wiring, me thinks. LOL
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Kyle-
2004 Rainier
1970 Chevelle - Resto
1974 K5 Blazer - Resto
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RE: Tranny wont downshift - 10/9/2007 7:06:47 AM
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bitbandit
Posts: 102
Joined: 9/16/2007
From: Brigham City, UT
Status: offline
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oh, i was looking at the wiring on the wrong sensor for the ECT then, where on the intake is the ECT at?
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RE: Tranny wont downshift - 10/9/2007 7:08:03 AM
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bitbandit
Posts: 102
Joined: 9/16/2007
From: Brigham City, UT
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if one of these two is acting up will it effect the other since they share the same ground ?
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RE: Tranny wont downshift - 10/9/2007 7:19:32 AM
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swartlkk
Posts: 14308
Joined: 5/1/2005
From: Waterloo, NY
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Sorry, the ECT is in the driver's side cylinder head. Looking back over my references, I can not find a clear answer as to where the gauge sensor is located, but I suspect it is in the passenger side cylinder head. At any rate, the ECT will be a two wire sensor and should be on the driver's side cylinder head between the back two cylinders.
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Kyle-
2004 Rainier
1970 Chevelle - Resto
1974 K5 Blazer - Resto
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RE: Tranny wont downshift - 10/9/2007 7:26:30 AM
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bitbandit
Posts: 102
Joined: 9/16/2007
From: Brigham City, UT
Status: offline
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ok, so i was looking at the correct one, i am not looking forward ot changing it if i need to, its in a lame spot, looks about as bad as the 3rd spark plug...
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2001 ZR2 Auto. Trans.
AirRaid Intake
March Pulleys
W4M Tune
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