Rusty Nellz

My son bought a 1996 5.7 Silverado. Obd listed ever transmission code imaginable when he bought it. Dropped the pan replaced all solenoids and wiring harness. New obd is p0758 electrical. Starts off and stays in 3rd gear will not go to overdrive. Replaced ignition switch. Ssdd. Trying to figure out where to go from here. Any suggestions appreciated. Gonna be a new truck when I get thru.

PNW NBS Z71

Welcome to the forum from Oregon.

Found this and you may have a valve body problem:

P0758 code definition

When a P0758 code is set in an automatic transmission vehicle, it shows that the actual gear that the vehicle is currently using differs from the gear that the PCM (powertrain control module) requires.

What the P0758 code means

Shift solenoid B allows the transmission to shift between second and third gear. If the PCM records code P0758, it indicates that the PCM cannot see the proper change in engine RPMs or the correct increase in road speed that should be happening during a shift from second to third gear.

What causes the P0758 code?

A number of issues can cause the PCM to record a P0758 code, including:

• Shift solenoid B is faulty.
• The wiring or connector for shift solenoid B is loose, shorted, or open.
• The valve body is defective.
• The transmission fluid is low and/or contaminated.

What are the symptoms of the P0758 code?

Once the P0758 code has been detected and stored, the Check Engine light will illuminate. The driver may also notice a few other symptoms:

• Inability to shift from second to third gear correctly
• Decreased fuel efficiency

In some cases, the engine may seem to misfire, but it is likely not an engine misfiring problem, but rather an issue with the shift solenoid or related components. In very rare cases, there will be no noticeable symptoms, other than the Check Engine light coming on.

How does a mechanic diagnose the P0758 code?

In addition to checking which codes have been recorded by the PCM, using an OBD-II scanner, the mechanic should also record all information associated with the circumstances under which the code was set. Then, after clearing the code(s), they should take the vehicle for a brief test drive to try to duplicate the conditions of the code being set. They will typically need to gently accelerate the vehicle to between 15 and 35 miles per hours, and they’ll need to watch the scanner and see if the PCM is able to send the signal to shift solenoid B to tell it to shift.

After this test drive, they’ll do a visual inspection of all related wiring and connectors, check for voltage drops in the shift solenoid, and check the level of the transmission fluid. If they transmission fluid looks contaminated, they will flush and replace it, and then retest the system once more.

Common mistakes when diagnosing the P0758 code

Because the noticeable symptoms of this problem can resemble an engine misfiring issue, it’s easy to misdiagnose it as a problem with the driveline or with the engine’s ignition timing.

How serious is the P0758 code?

Being unable to shift from second to third can result in a number of problems for an automatic transmission vehicle, and it can pose a hazard when driving, as well. To ensure that you are safe and that your vehicle is able to run reliably, you should get this problem taken care of immediately.

What repairs can fix the P0758 code?

In most cases, one or more of the following repairs will be necessary to resolve a P0758 code:

• Replacing a faulty shift solenoid.
• Replacing a defective valve body.
• Repairing or replacing damaged wiring or connectors.
• Adding more transmission fluid or changing out contaminated transmission fluid.