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Old 10-23-2002, 08:40 PM   #1
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Join Date: Aug 2001
Location: Spartanburg, SC
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My check engine light has been on all weekend, I went to autozone today and pulled the codes.

As expected I got P0404, EGR flow ckt range/perf. I figured this means due to my limited EGR, the computer dosent think its getting enough EGR gasses. Easy fix, I'll just drill it out a little this weekend.

But then to my suprise, I got a PO751, Shift Solinoid A ckt perf or stuck off.

So I wrote them down and then erased them. The 25 mi. drive to my moms house to drop off my son it didnt come back on. When I was going from her house back to the interstate it came back on. Well on the 40 mi. trip to work it went back off, so I figure it was b/c of the EGR again. I'm gonna pull the limiter back off this weekend and drill it out a little.

I autocrossed on sunday and left the tranny in 2nd. Ran four laps the same way and so did my co-driver for a total of 8 laps. I didnt have any problems at Turner feild when I raced and I ran one lap there in 1st, but only had four laps that time.

Anyway to make a long story short, what does the PO751 involve and can I fix it myself, with the factory service manuals? I changed the tranny fluid about 5k ago, its full, smells fine and the truck is running and shifting fine as well. Should I ingnore it or what?? When the light came on (last friday) I was making a left hand turn and the truck bogged down to about 2-300 rpm and almost cut off, but I punched the gas and it stayed running? Other than that one time its been fine ever since?

sorry for the novel.

'98 Silverado Z71 ECSB 5.7L/4L60E/3.73's-sold

'02 Suburban 5.3L/4L60E/3.73's -crashed

'78 GMC Serria 1500 361/NV3500/3.73

'00 Indigo Blue Xtreme 262/4L60E/3.42--SOLD
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Old 10-23-2002, 08:50 PM   #2
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Join Date: Apr 2002
Location: Richmond, VA
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The 1-2 Shift Solenoid (SS) valve controls the fluid flow acting on the 1-2 and 3-4 shift valves. The solenoid is a normally-open exhaust valve. With the 2-3 SS valve, the 1-2 SS valve allows four different shifting combinations.

When the VCM detects a 1-1-4-4 or a 2-2-3-3 shift pattern, depending on the state of the mechanical failure, then DTC P0751 sets. DTC P0751 is a type A DTC.


No TP sensor DTCs P0122 or P0123.
No VSS assembly DTCs P0502 or P0503.
No TCC solenoid valve DTC P0740.
No TCC stuck ON DTC P0742.
No 1-2 SS valve DTC P0753.
No 2-3 SS valve DTC P0758.
No 3-2 SS valve assembly DTC P0785.
No TFP manual valve position switch DTC P1810.
No TCC PWM solenoid valve DTC P1860.
The engine speed is greater than 450 RPM for 5 seconds .
The engine is not in fuel cutoff.
The vehicle speed is greater than 8 km/h (5 mph ).
The TP angle is 10-35% .
The TP angle is constant within 7% .
The gear range is D4.
The transmission fluid temperature is 20-130C (68-266F) .
The VCM commands a 1-2, 2-3 and 3-4 shift.
The TCC is commanded ON.
DTC P0751 sets if the following conditions occur three times:

Within 2 seconds , the engine speed in 2nd gear is 80 RPM greater than the last speed in 1st gear.
Within 2 seconds , the engine speed in 3rd gear is 100 RPM less than the last speed in 2nd gear.
Within 2 seconds , the engine speed in 4th gear is 10 RPM greater than the last speed in 3rd gear.
All of the above conditions are met and one of the following conditions occurs:

Condition 1

The speed ratio is 0.85 to 1.2 (speed ratio is engine speed divided by transmission output speed).
The TCC slip speed is 200-1000 RPM for 4 seconds .
Condition 2

The speed ratio is 0.6 to 0.8.
The TCC slip speed is -20 to +50 RPM for 4 seconds .

The VCM illuminates the Malfunction Indicator Lamp (MIL) .
The VCM commands D2 line pressure.
The VCM freezes shift adapts from being updated.
The VCM records the operating conditions when the Conditions for Setting the DTC are met. The VCM stores this information as Freeze Frame and Failure Records.
The VCM stores DTC P0751 in VCM history.

The VCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
A scan tool can clear the MIL/DTC.
The VCM clears the DTC from VCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
The VCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the VCM.

Verify that the transmission meets the specifications in the Shift Speed table.
Other internal transmission failures may cause more than one shift to occur.
Refer to the Shift Solenoid Valve State and Gear Ratio table



se if that helps
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