Camaro and Firebird: Why Am I Receiving Autotap Code P1870?

This article applies to the Camaro and Firebird (1990-2002), as well as the Chevrolet Corvette (1998-2004).

So you have received the dreaded P1870 CEL code. Everything you have been told or you might have read probably has scared you and your wallet to death. Many professional shops will tell you that you need a complete transmission rebuild and want to charge you upwards of $2,000 to do it. This may not be the case, especially if you haven't ignored the code hoping it would magically disappear. If you catch this code soon enough, which is about the time when you feel hard shifting from first to second gear, the fix is relatively easy and inexpensive. GM released TSB 01-07-023A to address this issue and how to fix the problem. If you have a little bit of knowledge about transmissions and have the tools, you can resolve the problem which is a replacement of a control valve body by purchasing and installing an inexpensive repair kit. Many transmissions shops will tell you to not do that and they'll replace or rebuild your tranny for you at a really high cost. If you happen to find one who will install the kit for you, it will be a fraction of the cost of a rebuild, but of course, several times higher than if you do the work yourself. It is a bit involved, so if you have any qualms at all about tearing into your transmission, don't give up until you find a pro who will install the kit for you.

Step 1 – Check your transmission fluid

If it is black or smells burnt, you have a big problem.

Very black and a burnt odor is very indicative that your transmission is shot. It is running way too hot, and the clutch is probably burnt up. A rebuild is likely necessary or a new install, which is probably more expensive. Unfortunately, there is not likely a way around this. To verify problems or concerns, you'll need to look in the transmission pan.

If the fluid is very dark or smells burnt, drop the pan and take a closer look.

Step 2 – Lift your car and remove the transmission pan

You need to inspect the fluid in the pan to determine the extent of the damage.

• Lift your car with a hydraulic floor jack.
• Place on jack stands in the approved locations.
• If you have four jack stands, it will be easier to lift the entire car, front and back. Use the highest position your jack stands will support.
• Locate the transmission drain pan and place a large catch pan underneath, as this is a messy job.
• Remove the 13mm mounting bolts for the transmission drain pan and drain it into your catch pan.
• Once the fluid has completely drained into your catch pan, carefully inspect it for color and smell and run a magnet through the old fluid.
• If you see large debris or shavings stuck to your magnet, that indicates internal damage to your transmission and it likely needs to be replaced or rebuilt at this point.

If your fluid is not black, burnt and no metal debris appeared, you are in luck.

Step 3 – Check out the TSB on this problem

GM released TSB 01-07-30-023A on how to address this issue.

Your P1870 code was likely triggered because of wear in the control valve body that contains the TCC isolator and regulator valves. This in turn causes your hard first to second up shifting. If all the following conditions have not been observed, you will likely only need to replace the valve body and not have to replace or rebuild your transmission.

• On cold starts and before the car reaches operating temperature, you do not notice any slips or missing gear shifts.
• The torque converter did not overheat (you can only see this upon inspection).
• You have already verified in the previous steps that your transmission fluid is not black or smell burnt and no shavings are present.

If you met the conditions above, you should be extremely relieved that this isn't going to cost you an arm and a leg.

Step 4 – Install a shift kit package to fix the code

There are many on the market, but in particular, many owners have found success with TransGo and Sonnax.

You will need to remove your valve body from the transmission, which is found under the transmission filter, which is accessed by removing the transmission pan. Once you have the valve body removed and on a bench, you can then remove and replace the control valve shift kit that you purchased to solve the P1870 code.

• Disconnect the electrical connection to the transmission.
• Remove the transmission pan (sixteen 13mm bolts).
• Remove the large flat transmission filter (you may consider replacing this filter since you have it off anyway).
• Disconnect the wiring harness, making note of the color of wires from each of the two harnesses going into the two solenoids.
• Remove the lockup solenoid (two bolts). (For later models, you may have to remove the PWM and TCC solenoids first (clip connector).)
• Disconnect the force motor.
• Remove the pressure manifold switch (five bolts).
• Remove the Detent level (one bolt in center).
• Remove the 14 bolts holding the valve body in. Three of these bolts are 8mm, the rest are 10mm.
• When removing the valve body, be very careful that you do not lose any of the 1/4" checkballs that are located underneath.
• Place the valve body on your work bench and replace the bad valves, following the instructions with the kit you purchased.
• Replace the valve body and follow these steps in reverse to put her back together.

This should clear your P1870 code.

Step 5 – Time for a test drive

The P1870 code will kick off only with two consecutive start and drive cycles.

You will need to do a test drive to make sure that your code resets and doesn't come back. Make sure your test drive utilizes an incline, such as an off-ramp from a freeway. You may need to make two test drives, completely stopping and turning off your car in between to ensure that your problem is fixed and doesn't return. You should definitely have better shifting now.

Featured Videos: 4L60E Transmission Repair Options

• 4L60E Valve Body Removal and Shift Kit

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