P1870 GM: transmission component slipping, usually at the torque converter clutch

Transmission component slipping (GM)

P1870 in short

On Chevrolet and GMC vehicles, P1870 means the computer saw too much slip once the torque converter clutch was locked in a high gear. Worn valve body bores, the converter clutch and its solenoid are the usual causes. It often brings a harsh 1-2 shift. Have it inspected soon.

At cruise the torque converter clutch locks the engine to the transmission so there is almost no slip. GM's computer compares engine speed with transmission output speed after commanding the clutch on in high gear; if slip stays above a limit (about 180 rpm for several seconds on some units), it sets P1870.

To protect the transmission, the computer then raises line pressure and stops applying the converter clutch, and may block 4th gear. Higher pressure is why many owners first notice a harsh 1-2 upshift. The check engine light may not come on with this code on some vehicles.

The code applies to GM 4L60-E, 4L80-E, 4L30-E and 4T60-E transmissions. Trade sources say the most common cause is wear in the valve body bores that control the converter clutch; a cracked converter piston on the 4L80-E and clutch or band slip on the 4L60-E can also set it.

Pick your make

P1870 is a manufacturer-specific code: its meaning depends on who built the car.

Other makes: meaning not verified. Check with a scan tool that reads manufacturer definitions.

Most likely causes

  1. Worn valve body bores controlling the converter clutch

    Common general cause
    Why it ranks here
    Trade references name wear in the converter clutch regulator, isolator, actuator feed limit and converter clutch valve bores as the most common cause.
    What would change this
    Rises on a high-mileage unit with harsh 1-2 shifts and no internal slip in the gears.

  2. Torque converter clutch failure (for example a cracked piston on the 4L80-E)

    Supported by vehicle data
    Why it ranks here
    GM has a bulletin for harsh converter clutch apply and P1870 on 2000–2001 4L80-E trucks, and trade sources note cracked converter pistons on that unit.
    What would change this
    Rises on a 4L80-E truck, or if slip is seen only with the converter clutch applied.

  3. Converter clutch solenoid or its hydraulic circuit

    Common general cause
    Why it ranks here
    Trade sources list the converter clutch solenoid, orifices and pump seals among causes.
    What would change this
    Rises if converter clutch codes such as P0741 are stored too.

  4. Low transmission fluid

    Common general cause
    Why it ranks here
    Low fluid is the simplest cause trade sources list for slip that sets P1870.
    What would change this
    Rises if the fluid level is low or there is a leak.

  5. 3-4 clutch or 2-4 band slip (4L60-E)

    Possible — needs testing
    Why it ranks here
    Trade sources note that slip in the 3-4 clutch or 2-4 band on the 4L60-E also sets P1870, since the computer sees slip in high gear.
    What would change this
    Rises if the transmission flares or slips on the 2-3 or 3-4 shift.

  6. Setup after a transmission or converter replacement

    Supported by vehicle data
    Why it ranks here
    GM has information for harsh 1-2 upshifts and the check engine light after a transmission or converter replacement on its trucks and vans, and trade sources list reprogramming among causes.
    What would change this
    Rises if the code appeared soon after a transmission or converter was replaced.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Check the transmission fluid level and condition with the engine running and the fluid warm, following the owner's manual.

    Use cautionTool: dipstick

    Warning:The engine runs during this check. Keep hands and clothing clear of the fan and belts, and the fluid and dipstick tube can be hot.

  2. Read all codes and note whether the transmission or converter was recently replaced.

    Low riskTool: scan tool

  3. Have a shop watch converter slip and clutch command on a scan tool at cruise in high gear, then inspect the valve body or converter as needed.

    Best left to a shopTool: scan tool with transmission data

    Warning:Shop job. Road testing with live data needs a second person, and valve body and converter work is internal transmission repair.

Symptoms

  • Harsh 1-2 upshift
  • Torque converter clutch no longer locks, so cruise rpm is higher
  • Check engine light, though on some vehicles it may not come on
  • No 4th gear, or transmission stuck in one gear Gets more serious: stop and have it checked.

How to fix

  1. Check the fluid level first and top up only with the specified fluid.

  2. Ask a shop that knows GM transmissions about valve body wear before agreeing to a full rebuild or new converter.

Parts and cost context

  • Transmission control module (TCM):P1870 reports real slip; replacing the computer does not fix it unless a reprogram is part of a documented repair.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Chevrolet

  • 2000–2001 · Silverado 1500

    Supported by vehicle data

    GM 3047 covers harsh converter clutch apply and/or P1870 on the 4L80E in Silverado, Suburban and Express. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

  • 1996–2000

    Supported by vehicle data

    GM 01-07-30-023B covers a harsh 1-2 upshift with P1870 on Chevrolet and GMC trucks, Camaro and Corvette. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

  • 1997 · Camaro

    Supported by vehicle data

    GM 97-12-01-777-17A covers converter clutch slip and/or P1870 at 45–55 mph. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

  • 020730001AStatus unverified

    DTC P1870, transmission component slipping

    2000–2002 · issued · NHTSA 628845

    Diagnostic information on P1870 for 2000–2002 passenger cars and light trucks, later updated to include 2004 models. GMC, Buick and Cadillac are also listed. Only the NHTSA flat-file summary was reviewed, not the bulletin itself.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • 010730023BStatus unverified

    Harsh 1-2 upshift with the MIL and P1870

    1996–2000camaro, corvette · issued · NHTSA 634815

    Some customers may report a harsh 1-2 upshift with the check engine light on and P1870 set. Chevrolet and GMC trucks are also listed. Only the NHTSA flat-file summary was reviewed, not the bulletin itself.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • 3047Status unverified

    Harsh TCC apply and/or P1870, 4L80E

    2000–2001express, silverado-1500, suburban · issued · NHTSA 10009392

    Covers harsh converter clutch apply and/or P1870 on the 4L80E. The GMC Savana, Sierra 1500 and Yukon are also listed. Only the NHTSA flat-file summary was reviewed, not the bulletin itself.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • PIP5340AStatus unverified

    Harsh 1-2 upshift and MIL after transmission or converter replacement

    1998–2006astro, blazer, express, s10, silverado-1500 · issued · NHTSA 10096073

    After a transmission or torque converter replacement the vehicle may have a harsh 1-2 upshift and the check engine light on. GMC models are also listed. Only the NHTSA flat-file summary was reviewed, not the bulletin itself.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • 97120177717AStatus unverified

    TCC slip and/or P1870 at 45–55 mph

    1997camaro · issued · NHTSA 54010

    Covers slip and/or P1870 at 45–55 mph when the converter clutch applies. Only the NHTSA flat-file summary was reviewed, not the bulletin itself.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

GMC

  • 2000–2001 · Sierra 1500

    Supported by vehicle data

    GM 3047 covers harsh converter clutch apply and/or P1870 on the 4L80E; the Savana and Yukon are also listed. The bulletin is on NHTSA, but whether it is still current is not verified, so it is labelled vehicle data rather than confirmed.

  • P0741Torque converter clutch not engaging as commanded

    Same system Possible — needs testing

    P0741 is the generic converter clutch performance or stuck-off code. Trade sources cover it with P1870, and the same worn converter clutch valves can set either.

All Transmission codes

P1870 questions

Why is my 1-2 shift harsh with P1870?

When P1870 sets, GM's computer raises line pressure to protect the transmission. Higher pressure makes shifts, especially 1-2, much firmer.

Does P1870 mean I need a new transmission?

Not necessarily. Trade sources say the most common cause is wear in the valve body bores that control the converter clutch, which is repaired without replacing the whole transmission.

Sources and review

  1. Deciphering GM Transmission DTC P1870 — MOTOR Magazine (Wayne Colonna) ,
  2. Beyond 1870: GM Converter Codes P0741, P0742 and 1887 — Sonnax (Gregg Nader) ,
  3. Cal. Code Regs. Tit. 13, § 1968.2 — Malfunction and Diagnostic System Requirements (OBD II) — California Air Resources Board (via Cornell LII)
  4. GM 3047: harsh TCC apply and/or DTC P1870, 4L80E — General Motors ,
  5. GM PIP5340A: harsh 1-2 upshift and MIL after transmission or converter replacement — General Motors ,
  6. GM 01-07-30-023B: harsh 1-2 upshift, MIL and DTC P1870 — General Motors ,
  7. GM 97120177717A: 1997 Camaro TCC slip and/or DTC P1870 at 45–55 mph — General Motors ,
  8. GM 02-07-30-001A: DTC P1870, transmission component slipping — General Motors ,
Last reviewed
Written by
Saurabh K.
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