Transmission slips?

Chemicals, (aka "mechanic in a can"), rarely solve problems. They aren't going to repair a mechanical problem. Slippage in a transmission is almost always caused by worn clutch plates, and it needs to be rebuilt to solve that. If you really want to buy a car with problems, get a quote for a worst-case cost from a transmission specialty shop, then deduct that amount from the value of the car to determine what it's worth. If this would be an easy fix, the current owner would have done it before selling the car or instead of selling it.

This guide can help us fix the problem

https://www.2carpros.com/articles/automatic-transmission-problems

Please run down this guide and report back.

Hi David,

Does the D4 light blinks while driving?

Code 1 = Defective Lock-up Control Valve or its wiring circuit.

It should not be related to the non shifting and is more likely to be an after effect.

Is it a quick or prolonged link? 1 and 10 are different problems.

The other possibility is a faulty TCM.

That means a code 1.

A fault with the lock up clutch system.

One of the common fault for the problem would be a faulty TPS which does not show any code.

Another possible cause would be the TCM

Hi rjblank,

If the trans throttle pressure cable is faulty or incorrectly adjusted, it would either shift too early and slip under load or it would shift late and shifts harshly.

A faulty Throttle Position Sensor would cause erratic shifting as well.

If you are able to use a DVOM, you can test the TPS voltage either at the ECU or the TPS sensor. To test via the TPS sensor you would need to make an adapter or extend the wires to be able to test the voltage.

If the ECU is used for testing the voltage, you can use the DVOM to back probe the terminals but you would need an assistant to operate the accelerator.

Hi carljrus,

At the throttle body there are 2 cables, one for the accelerator and the other leading to the transmission, just below the lower radiator hose.

This is known as the throttle pressure cable and it controls the transmission line pressure.

The throttle lever at transmission side should start opening as soon as the throttle starts to open. If the cable is adjusted too short, there would be excessive line pressure resulting in harsh shifting.

If the cable is too long, pressure would be low resulting is slipping or flaring at moment of upshift and downshift would be delayed with lack of accelerating power.

At the throttle side, note if there is any slack in the trans throttle cable. If none, release the lock nut at transmission end and adjust until there is only minimal slack. Slowly turn the throttle opener and note the movement of the trans throttle cable.

Trans lever should start moving nly when the throttle plate starts opening, not before or after. Some testing and readjustment might be required to get the correct setting.

Apart from throttle cable out of adjustment, fluid condition, engine mounts, throttle position sensor and trans internal faults can cause harsh shifting.

If harsh shifting only occurs for specific speeds, then it is the clutch concerned that is faulty.

I would say rebuilding is not a DIY job in terms of difficulty. Special tools would be required.

Hi fivekcar,

Thank you for the donation.

You are not experiencing clutch slippage, rather it is a case of idling surging. Check for vacumn leakages.

Since the trans is shifting hard, check the trans throttle pressure cable adjustment. It might have been adjusted too short resulting in too high pressure when upshifting.

Check the engine mounts too.

Hi br5499williams,

When the D4 light blinks, it means an error has been detected by the TCM. You need to retrieve the DTC to find out what is causing it.

Count the flashes of the D4 light with ignition switch ON and let me know.
Prolonged flashes = 10
Short quick flash = 1